Add FAQ about why stop, restart, add/remove_handler could make the co…

…de hang

docs/source/faq.rst

@@ -253,6 +253,19 @@ contact people using official apps. The answer is the same for Pyrogram too and
 for usernames, meeting them in a common group, have their phone contacts saved or getting a message mentioning them,
 either a forward or a mention in the message text.
 
+Code hangs when I stop, restart, add/remove_handler
+---------------------------------------------------
+
+You tried to ``.stop()``, ``.restart()``, ``.add_handler()`` or ``.remove_handler()`` *inside* a running handler, but
+that can't be done because the way Pyrogram deals with handlers would make it hang.
+
+When calling one of the methods above inside an event handler, Pyrogram needs to wait for all running handlers to finish
+in order to safely continue. In other words, since your handler is blocking the execution by waiting for the called
+method to finish and since Pyrogram needs to wait for your handler to finish, you are left with a deadlock.
+
+The solution to this problem is to pass ``block=False`` to such methods so that they return immediately and the actual
+code called asynchronously.
+
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