Revised the documentation.

docs/source/index.rst

@@ -6,6 +6,12 @@
 Welcome to Flask-Digest-Auth's documentation!
 =============================================
 
+*Flask-Digest-Auth* is an `HTTP Digest Authentication`_ implementation
+for Flask_ applications.  It authenticates the user for the protected
+views.
+
+HTTP Digest Authentication is specified in `RFC 2617`_.
+
 .. toctree::
    :maxdepth: 2
    :caption: Contents:
@@ -22,3 +28,7 @@ Indices and tables
 * :ref:`genindex`
 * :ref:`modindex`
 * :ref:`search`
+
+.. _HTTP Digest Authentication: https://en.wikipedia.org/wiki/Digest_access_authentication
+.. _RFC 2617: https://www.rfc-editor.org/rfc/rfc2617
+.. _Flask: https://flask.palletsprojects.com