Clean up and complete RTD documentation

readthedocs/extra/advanced-usage/sessions.rst

@@ -0,0 +1,46 @@
+.. _sessions:
+
+==============
+Session Files
+==============
+
+The first parameter you pass the the constructor of the ``TelegramClient`` is
+the ``session``, and defaults to be the session name (or full path). That is,
+if you create a ``TelegramClient('anon')`` instance and connect, an
+``anon.session`` file will be created on the working directory.
+
+These database files using ``sqlite3`` contain the required information to
+talk to the Telegram servers, such as to which IP the client should connect,
+port, authorization key so that messages can be encrypted, and so on.
+
+These files will by default also save all the input entities that you've seen,
+so that you can get information about an user or channel by just their ID.
+Telegram will **not** send their ``access_hash`` required to retrieve more
+information about them, if it thinks you have already seem them. For this
+reason, the library needs to store this information offline.
+
+The library will by default too save all the entities (chats and channels
+with their name and username, and users with the phone too) in the session
+file, so that you can quickly access them by username or phone number.
+
+If you're not going to work with updates, or don't need to cache the
+``access_hash`` associated with the entities' ID, you can disable this
+by setting ``client.session.save_entities = False``, or pass it as a
+parameter to the ``TelegramClient``.
+
+If you don't want to save the files as a database, you can also create
+your custom ``Session`` subclass and override the ``.save()`` and ``.load()``
+methods. For example, you could save it on a database:
+
+    .. code-block:: python
+
+        class DatabaseSession(Session):
+            def save():
+                # serialize relevant data to the database
+
+            def load():
+                # load relevant data to the database
+
+
+You should read the ````session.py```` source file to know what "relevant
+data" you need to keep track of.