Add common issues to read.me (#668)

* Add common issues to read.me

The issue that a POST is not working, seems to
came up very offten in the issue section.
Therefore this commit integrates that into the
readme.md

I also replaced `getLocalizedURL` with `localizeURL`
because its shorter, and I think most people
just want to pass the `url` anyway.

* Added not obvious duplicates of post-issue

* grammatically adjustments

Author: niels-numbers

README.md

@@ -28,8 +28,12 @@ Ask [mcamara](https://github.com/mcamara) if you want to be one of them!
     - <a href="#route-model-binding">Route Model Binding</a>
 - <a href="#translated-routes">Translated Routes</a>
 - <a href="#caching-routes">Caching routes</a>
-- <a href="#testing">Testing</a>
 - <a href="#changelog">Changelog</a>
+- <a href="#testing">Testing</a>
+- <a href="#common-issues">Common Issues</a>
+    - <a href="#post-is-not-working">POST is not working</a>
+    - <a href="#methodnotallowedhttpexception">MethodNotAllowedHttpException</a>
+    - <a href="#validation-message-is-only-in-default-locale">Validation message is always in default locale</a>
 - <a href="#license">License</a>
 
 ## Laravel compatibility
@@ -252,29 +256,31 @@ LaravelLocalization::getLocalizedURL('uk', 'a/b/c'); // http://url-to-laravel/uk
 
 This package comes with some useful functions, like:
 
-### Get URL for an specific locale
+
+### Get localized url
 
 ```php
-/**
- * Returns an URL adapted to $locale
- *
- * @param  string|boolean 	$locale	   	Locale to adapt, false to remove locale
- * @param  string|false		$url		URL to adapt in the current language. If not passed, the current url would be taken.
- * @param  array 		$attributes	Attributes to add to the route, if empty, the system would try to extract them from the url.
- *
- * @throws UnsupportedLocaleException
- *
- * @return string|false				URL translated, False if url does not exist
- */
-public function getLocalizedURL($locale = null, $url = null, $attributes = array())
+    /**
+     * Returns an URL adapted to $locale or current locale.
+     *
+     * @param string      $url    URL to adapt. If not passed, the current url would be taken.
+     * @param string|bool $locale Locale to adapt, false to remove locale
+     *
+     * @throws UnsupportedLocaleException
+     *
+     * @return string URL translated
+     */
+    public function localizeURL($url = null, $locale = null)
+```
 
 //Should be called in a view like this:
-{{ LaravelLocalization::getLocalizedURL(optional string $locale, optional string $url, optional array $attributes) }}
-```
+{{ LaravelLocalization::localizeURL('/about') }}
+
 
-It returns a URL localized to the desired locale.
+It returns a URL localized to the desired locale (if no locale is given, it uses current locale).
 
-##### Route Model Binding
+
+#### Route Model Binding
 
 Note that [route model binding]([https://laravel.com/docs/master/routing#route-model-binding]) is taken into account when generating the localized route.
 
@@ -293,7 +299,7 @@ Note that [route model binding]([https://laravel.com/docs/master/routing#route-m
 public function getNonLocalizedURL($url = null)
 
 //Should be called in a view like this:
-{{ LaravelLocalization::getNonLocalizedURL(optional string $url) }}
+{{ LaravelLocalization::getNonLocalizedURL('/es/about') }}
 ```
 
 It returns a URL clean of any localization.
@@ -315,7 +321,7 @@ It returns a URL clean of any localization.
 public function getURLFromRouteNameTranslated($locale, $transKeyName, $attributes = array())
 
 //Should be called in a view like this:
-{{ LaravelLocalization::getURLFromRouteNameTranslated(string $locale, optional array $transKeyNames, optional array $attributes) }}
+{{ LaravelLocalization::getURLFromRouteNameTranslated('es', 'routes.about') }}
 ```
 
 It returns a route, localized to the desired locale using the locale passed. If the translation key does not exist in the locale given, this function will return false.
@@ -567,10 +573,50 @@ More information on support on [cached (translated) routes here](CACHING.md).
 
 Note that the separate [czim/laravel-localization-route-cache](https://github.com/czim/laravel-localization-route-cache) package is no longer required.
 
+## Common Issues
+
+### POST is not working
+
+This may happen if you do not localize your action route that is inside your `Routes::group`.
+This may cause a redirect, which then changes the post request into a get request.
+To prevent that, simply use the [localize helper](#get-localized-url).
+
+For example, if you use `Auth::routes()` and put them into your `Route::group` Then
+
+```
+<form action="/logout" method="POST">
+<button>Logout</button>
+</form>
+```
+
+will not work. Instead, one has to use
+
+```php
+<form action="{{  \LaravelLocalization::localizeURL('/logout') }} " method="POST">
+<button>Logout</button>
+</form>
+```
+
+### MethodNotAllowedHttpException
+
+If you do not localize your post url and use a redirect middleware,
+then the post request gets redirected as a get request.
+If you have not defined such a get route, you will cause this exception.
+
+To localize your post url see the example in [POST is not working](#post-is-not-working).
+
+### Validation message is only in default locale
+
+This also happens if you did not localize your post url.
+If you don't localize your post url, the default locale is set while validating,
+and when returning to `back()` it shows the validation message in default locale.
+
+To localize your post url see the example in [POST is not working](#post-is-not-working).
+
 ## Testing
 
 During the test setup, the called route is not yet known. This means no language can be set.
-When a request is made during a test, this results in a 404 - without the prefix set the localised route does not seem to exist.
+When a request is made during a test, this results in a 404 - without the prefix set the localized route does not seem to exist.
 
 To fix this, you can use this function to manually set the language prefix:
 ```php