Add improved docs for slash commands (#77)

* Fix command checks actually working

* Current progress on slash command docs

* Improve docs for slash commands further

docs/ext/commands/slash-commands.rst

@@ -0,0 +1,23 @@
+.. currentmodule:: discord
+
+.. _ext_commands_slash_commands:
+
+Slash Commands
+==============
+
+Slash Commands are currently supported in enhanced-discord.py using a system on top of ext.commands.
+
+This system is very simple to use, and can be enabled via :attr:`.Bot.slash_commands` globally,
+or only for specific commands via :attr:`.Command.slash_command`.
+
+There is also the parameter ``slash_command_guilds`` which can be passed to either :class:`.Bot` or the command
+decorator in order to only upload the commands as guild commands to these specific guild IDs, however this
+should only be used for testing or small (<10 guilds) bots.
+
+If you want to add option descriptions to your commands, you should use :class:`.Option`
+
+For troubleshooting, see the :ref:`FAQ <ext_commands_slash_command_troubleshooting>`
+
+.. admonition:: Slash Command Only
+
+    For parts of the docs specific to slash commands, look for this box!