document how to get a token for bot creation

docs/setup.md

+# Matrix Backend Setup
+
+## Setup steps
+This is the 'standard' way Matrix bots tend to be setup. It's a little more involved than IRC, but still not
+too bad.
+
+### 1. Create an account for the Bot
+Give it a strong password, you can create a strong password on the command line using something like this:
+`pwgen -s 64 1`.
+
+If you are using the (rather fantastic) `matrix-docker-ansible-deploy` this will make an account:
+
+```
+ansible-playbook -i inventory/hosts setup.yml --extra-vars='username=errbot password=PASSWORD_FOR_THE_BOT admin=no' --tags=register-user
+```
+
+Else, you can use the admin API, a client, or synapse-admin web interface.
+
+### 2. Get an access token
+If you give the bot an access token and server address, it can figure pretty much everything else out for
+itself (device id, username, etc...).
+
+You can do this using any HTTP client, for example curl:
+
+```curl -X POST --header 'Content-Type: application/json' -d '{
+    "identifier": { "type": "m.id.user", "user": "errbot" },
+    "password": "PASSWORD_FOR_THE_BOT",
+    "type": "m.login.password"
+}' 'https://matrix.example.com/_matrix/client/r0/login'
+```
+
+### 3. Use the access token to connect
+If you're using our docker image, set the environment varible in your docker-compose:
+
+```
+version: '3'
+
+services:
+  xmpp:
+    image: "git.fossgalaxy.com:8042/irc/errbot/fg-errbot:matrix"
+    environment:
+      TZ: Europe/London"
+      BOT_SERVER: 'https://matrix.example.com'
+      BOT_TOKEN: '<token from step 2>'
+      BOT_ADMINS: '@admin:example.com'
+    volumes:
+            - data:/home/errbot/bot/data
+    restart: unless-stopped
+
+volumes:
+        data:
+```
+
+If you're not, setup your config.py, for example:
+
+```
+import logging
+
+BACKEND = 'Matrix'
+BASE_DIR = "/path/to/bot/dir/"
+
+BOT_DATA_DIR = BASE_DIR + 'data/'
+BOT_EXTRA_PLUGIN_DIR = BASE_DIR + 'plugins/'
+BOT_EXTRA_BACKEND_DIR = BASE_DIR + 'backends/' # place where backend-matrix lives
+
+BOT_LOG_FILE = BASE_DIR + r'errbot.log'
+BOT_LOG_LEVEL = logging.DEBUG
+
+BOT_ADMINS = ('@admin:example.com', )
+
+BOT_IDENTITY = {
+    'homeserver': 'https://matrix.example.com',
+    'token': '<token from step 2>'
+}
+```
+
+That's it, now just do the standard errbot stuff (install plugins, etc...)
+
+If you are using matrix-registration and want errbot to manage registration tokens for you, check out our
+matrix errbot plugin. 
+
+## Acknowledgements
+* Some steps adapted from [matrix-docker-ansible-deploy](https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/docs/configuring-playbook-matrix-registration.md).
+