add extras role

roles/extras/templates/config/README.md

@@ -0,0 +1,34 @@
+Mautrix bridge config updates last checked on 2022-08-25
+To add a mautrix bridge, create a var file and based on an older one and a new config file like this:
+
+```
+{% extends 'mautrix-bridge.yaml.j2' %}
+
+{% block backfill %}
+{{ super() }}
+        additional options for the backfill section, needs to be indentded. Omit super()
+        above if the required options are different from the usual.
+{% endblock %}
+
+{% block bridge %}
+    additional options for the bridge section, needs to be indented
+{% endblock %}
+
+{% block additional %}
+additional sections here
+{% endblock %}
+
+```
+
+Any block can be omitted if not needed
+
+Available blocks in vars:
+```
+mautrix_blocks:
+  - public
+  - provisioning
+  - relay
+  - delivery_error_reports
+  - displayname_template
+  - backfill
+```