Issue #28: Create docs (troubleshooting).

docs/installation.rst

@@ -37,3 +37,15 @@ For versions that are not in Pypi (it is a development version)::
 If you do not have git installed::
 
     $ pip install https://github.com/Nekmo/gkeep/archive/<branch>.zip
+
+
+Troubleshooting
+---------------
+Gkeep is unstable because **it doesn't use an official Google api**. Before opening a new incident update gkeep and its
+dependencies to the latest version::
+
+    $ pip install -U gkeep --upgrade-strategy eager
+
+In case of problems with **authentication** check the credentials file in ``~/.config/gkeep/auth.json``. It is
+recommended to protect this file for security. Accounts with two-step authentication must use an application password.
+For more info: https://support.google.com/mail/answer/185833