Adds docs and empty inotify emitter implementation

Adds an automatic documentation entry into the
``docs/source/api.rst`` file for the
``watchdog.observers.inotify`` module.

Adds an empty inotify emitter module named
``watchdog.observers.inotify`` with documentation
about Linux versions, glibc versions, and emitter
implementation notes.

Signed-off-by: Gora Khargosh <gora.khargosh@gmail.com>