Small updates in readme and docs (#125)

- add info about installation with extra ([]session])
- add links to examples
- move `Public api` header into related section

docs/index.rst

@@ -3,16 +3,9 @@ aiohttp_security
 
 The library provides security for :ref:`aiohttp.web<aiohttp-web>`.
 
-Usage
------
 
-
-License
--------
-
-``aiohttp_security`` is offered under the Apache 2 license.
-
-Contents:
+Contents
+--------
 
 .. toctree::
    :maxdepth: 2
@@ -23,7 +16,10 @@ Contents:
    example_db_auth
    glossary
 
+License
+-------
 
+``aiohttp_security`` is offered under the Apache 2 license.
 
 Indices and tables
 ==================