Various improvements

docs/source/faq/sqlite3-operationalerror-database-is-locked.rst

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+sqlite3.OperationalError: database is locked
+============================================
+
+This error occurs when more than one process is using the same session file, that is, when you run two or more clients
+at the same time using the same session name or in case another program has accessed the file.
+
+For example, it could occur when a background script is still running and you forgot about it. In this case, you either
+restart your system or find and kill the process that is locking the database. On Unix based systems, you can try the
+following:
+
+#. ``cd`` into your session file directory.
+#. ``fuser my_account.session`` to find the process id.
+#. ``kill 1234`` to gracefully stop the process.
+#. If the last command doesn't help, use ``kill -9 1234`` instead.
+
+If you want to run multiple clients on the same account, you must authorize your account (either user or bot)
+from the beginning every time, and use different session names for each parallel client you are going to use.