docs: added difference between get_ commands and fetch_ commands in FAQ

docs/faq.rst

@@ -109,6 +109,17 @@ Putting both of these pieces of info together, you get the following: ::
     activity = discord.Activity(name='my activity', type=discord.ActivityType.watching)
     client = discord.Client(activity=activity)
 
+What is the difference between get_ methods and fetch_ methods?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+"Get" methods retrieve objects or data from the cache (general store of data) and can return ``None`` if not found. "Fetch" methods force an API request and will raise an error if not found. Example: ::
+
+        # --- Get example ---
+        role = member.guild.get_role(id)  # Try to get role without an API request through the cache
+        await member.add_roles(role)  # If the role is found, then it adds the role
+
+        # --- Fetch example
+        role = discord.utils.get(await member.guild.fetch_roles(), id=id)  # This will obtain the role via an API request
+
 How do I send a message to a specific channel?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~