Fix a typo & grammar in pull request template (#461)

* Fixed a typo

* Fixed grammar

Author: adamperkowski

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
 ## Type of Change
 - [ ] New feature
 - [ ] Bug fix
-- [ ] Documentation Update
+- [ ] Documentation update
 - [ ] Refactoring
 - [ ] Hotfix
 - [ ] Security patch
@@ -16,7 +16,7 @@
 ## Impact
 <!--[Discuss the impact of your changes on the project. This might include effects on performance, new dependencies, or changes in behaviour.]-->
 
-## Issue related to PR
+## Issues / other PRs related
 <!--[What issue/discussion is related to this PR (if any)]-->
 - Resolves #