Update spaces developer/admin docs

Author: fbacall

docs/mtessx.md

@@ -0,0 +1,33 @@
+# Multi-space TeSS
+
+A multi-space enabled TeSS will set the current space based on the Host header of the incoming request 
+(if there is a Space defined with that host, otherwise it will fallback to the default space).
+
+# Development
+
+To allow your local development server to respond to requests to these hosts, 
+edit your hosts file (`/etc/hosts` on Linux) to include something like the following, e.g.:
+
+```
+127.0.0.1	plants.mytess.training
+127.0.0.1	astro.mytess.training
+127.0.0.1	whatever.mytess.training
+```
+
+This will ensure that if you visit e.g. plants.mytess.training, your browser will route it to your local development server
+(you may need to restart your browser after changing the hosts file).
+
+To ensure your Rails application accepts requests to the hosts provided above, you will also need to create a 
+file `config/initializers/hosts.rb` and add the necessary hosts to Rails' config:
+
+```ruby
+Rails.application.config.hosts << '.mytess.training' if Rails.env.development?
+```
+
+# Production
+
+To run a multi-space TeSS instance in production you will need to:
+
+* Add a DNS record with a wildcard (e.g. *.mytess.training) to point your server
+* Configure your web server (e.g. Apache) to respond to requests to these wildcard domains (e.g. `ServerAlias *.mytess.training`)
+* Acquire a wildcard SSL certificate (e.g. via Let's Encrypt/Certbot: <https://certbot.eff.org/instructions?ws=apache&os=snap&tab=wildcard>)