docs: add content to 'Extending'

Author: rodrigomelo9

docs/extending.rst

@@ -1,2 +1,40 @@
 Extending
 =========
+
+1. Add support for the new tool:
+
+.. code-block:: python
+
+   pyfpga/templates/<NEWTOOL>.jinja
+   pyfpga/templates/<NEWTOOL>-prog.jinja
+   pyfpga/<NEWTOOL>.py
+
+2. Include the new tool on Factory:
+
+.. code-block:: python
+
+   pyfpga/factory.py
+
+3. Add tests and a tool mock-up:
+
+.. code-block:: python
+
+   tests/test_tools.py
+   tests/mocks/<NEWTOOL_EXECUTABLE>
+
+4. Updated the project's documentation:
+
+.. code-block:: python
+
+   README.md
+   docs
+
+5. [OPTIONAL] Add examples:
+
+.. code-block:: python
+
+   examples/sources/cons/<NEWBOARD>/timing.<EXT>
+   examples/sources/cons/<NEWBOARD>/clk.<EXT>
+   examples/sources/cons/<NEWBOARD>/led.<EXT>
+   examples/projects/<NEWTOOL>.py
+   examples/hooks/<NEWTOOL>.py