[V3 Docs] Add install guides to the documentation (#1005)

* [Docs] add install guides to the documentation

* formatting changes

docs/install_raspbian.rst

@@ -0,0 +1,39 @@
+.. raspbian install guide
+
+==================================
+Installing Red on Raspbian Stretch
+==================================
+
+---------------------------
+Installing pre-requirements
+---------------------------
+
+.. code-block:: none
+
+    sudo apt-get install python3.5-dev python3-pip build-essential libssl-dev libffi-dev git libav-tools libopus-dev unzip -y
+
+--------------
+Installing Red
+--------------
+
+:code:`pip3 install red-discordbot[voice]`
+
+----------------------
+Setting up an instance
+----------------------
+
+Run :code:`redbot-setup` and follow the prompts. It will ask first for where you want to
+store the data (the default is :code:`~/.local/share/Red-DiscordBot`) and will then ask
+for confirmation of that selection. Next, it will ask you to choose your storage backend
+(the default here is JSON). It will then ask for a name for your instance. This can be
+anything as long as it does not contain spaces; however, keep in mind that this is the
+name you will use to run your bot, and so it should be something you can remember.
+
+-----------
+Running Red
+-----------
+
+Run :code:`redbot <your instance name>` and run through the initial setup. This will ask for
+your token and a prefix.
+
+.. warning:: Audio will not work on Raspberry Pi's **below** 2B. This is a CPU problem and *cannot* be fixed.