(#130) Chain (Python): Resolve TODO. Add SimpleFilter tutorial reference. Fix minor typos in Chain and Cache tutorials

Signed-off-by: EsipovPA <esipov.p@mail.ru>

Author: EsipovPA

doc/Tutorials/Cache-Cpp.rst

@@ -293,7 +293,7 @@ Now open the ``CMakeLists.txt`` add the executable and name it ``cache_tutorial`
 
 	ament_auto_add_executable(cache_tutorial src/cache_tutorial.cpp)
 
-Finally, add the install(TARGETS…) section so ros2 run can find your executable:
+Finally, add the ``install(TARGETS…)`` section so ros2 run can find your executable:
 
 .. code-block:: CMake
 

doc/Tutorials/Chain-Cpp.rst

@@ -445,7 +445,7 @@ Now open the ``CMakeLists.txt`` add the executable and name it ``chain_tutorial`
 
 	ament_auto_add_executable(chain_tutorial src/chain_tutorial.cpp)
 
-Finally, add the install(TARGETS…) section so ros2 run can find your executable:
+Finally, add the ``install(TARGETS…)`` section so ros2 run can find your executable:
 
 .. code-block:: CMake
 

doc/Tutorials/Chain-Python.rst

@@ -11,8 +11,7 @@ It allows you to store an N-long set of filters inside a single structure, makin
 To demonstrate the functionality of the ``Chain`` filter in a more clear manner, we are going to add a custom filter to this tutorial.
 This is going to be the ``CounterFilter`` that will be counting the number of messages passing through it.
 This filter class will be a successor to the ``SimpleFilter`` class, but this is a topic for another tutorial.
-
-.. TODO: @EsipovPA: Add message_filters.SimpleFilter tutorial reference, when ready
+For more information on this topic, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.
 
 Prerequisites
 ~~~~~~~~~~~~~
@@ -174,8 +173,7 @@ The ``add`` method increases messages count, and passes messages to the followin
 The ``connectInput`` connects this filter to a previous filter's output.
 The ``counter`` property grants access to the current messages count.
 
-.. More on this succession mechanism should be in the corresponding tutorial
-.. TODO: @EsipovPA Add link to the message_filters.SimpleFilter tutorial, when added.
+For more information on this succession mechanism, please refer to the `SimpleFilter for Python tutorial <https://docs.ros.org/en/rolling/p/message_filters/doc/Tutorials/SimpleFilter-Python.html>`.
 
 And now we can turn our attention to the main tutorial class, that is the ``ChainNode`` class.
 For starters, let's take a look at the ``__init__`` method of this class: