Issue-374 Extend docs

Author: Rafal Mucha

CONTRIBUTING.rst

@@ -130,7 +130,7 @@ suite across the supported python versions.
 
   # install test requirements
   cd py4j-python
-  pip install -r requirements.txt
+  pip install -r requirements-test.txt
 
   # Run the full test suite
   nosetests

py4j-python/src/py4j/protocol.py

@@ -71,6 +71,8 @@
 PYTHON_PROXY_TYPE = "f"
 
 class TypeHint:
+    """Enables users to provide a hint to the Python to Java converter specifying the accurate data type for a given value.
+    Essential to enforce i.e. correct number type, like Long."""
     def __init__(self, value, java_type):
         self.value = value
         self.java_type = java_type

py4j-web/advanced_topics.rst

@@ -726,6 +726,27 @@ Java methods slightly less efficient because in the worst case, Py4J needs to
 go through all registered converters for all parameters. This is why automatic
 conversion is disabled by default.
 
+.. _explicit_conversion:
+
+Explicit converting Python objects to Java primitives
+-----------------------------------------------------
+
+Sometimes, especially when ``auto_convert=True`` it is difficult to enforce correct type 
+passed from Python to Java. Then, ``TypeHint`` from ``py4j.protocol`` may be used. 
+``java_type`` argument of constructor should be one of Java types defined in ``py4j.protocol``.
+
+So if you have method in Java like:
+
+.. code-block:: java
+
+  void method(HashSet<Long> longs) {}
+
+Then you can pass arguments with correct type to this method with ``TypeHint``
+
+::
+
+  >>> set_with_longs = { TypeHint(1, LONG_TYPE), TypeHint(2, LONG_TYPE) }
+  >>> gateway.jvm.my.Class().method(set_with_longs)
 
 .. _py4j_exceptions: