Document asyncio support

Signed-off-by: Bernát Gábor <gaborjbernat@gmail.com>

docs/index.rst

@@ -41,8 +41,6 @@ Installation
 Tutorial
 --------
 
-### Examples
-
 A :class:`FileLock <filelock.FileLock>` is used to indicate another process of your application that a resource or
 working directory is currently used. To do so, create a :class:`FileLock <filelock.FileLock>` first:
 
@@ -123,6 +121,12 @@ The :class:`SoftFileLock <filelock.SoftFileLock>` only watches the existence of
 portable, but also more prone to dead locks if the application crashes. You can simply delete the lock file in such
 cases.
 
+Asyncio support
+---------------
+
+This library currently does not support asyncio. We'd recommend adding an asyncio variant though if someone can make a
+pull request for it, `see here <https://github.com/tox-dev/py-filelock/issues/99>`_.
+
 Contributions and issues
 ------------------------