add title to docs/api.rst

Author: FoamyGuy

{{ cookiecutter.__dirname }}/docs/{% if cookiecutter.sphinx_docs in ['y', 'yes'] %}api.rst{% endif %}

@@ -4,5 +4,8 @@
 .. If your library file(s) are nested in a directory (e.g. /adafruit_foo/foo.py)
 .. use this format as the module name: "adafruit_foo.foo"
 
+API Reference
+#############
+
 .. automodule:: {% if cookiecutter.library_prefix %}{{ cookiecutter.library_prefix | lower }}_{% endif %}{{ cookiecutter.library_name | lower | replace(" ", "_") }}
     :members: