Add information about community-grouping for the Facebook bridge

docs/configuring-playbook-bridge-mautrix-facebook.md

@@ -43,6 +43,31 @@ https://matrix.DOMAIN/_matrix/client/r0/login
 - make sure you don't log out the `Mautrix-Facebook` device some time in the future, as that would break the Double Puppeting feature
 
 
+## Set up community-grouping
+
+This is an **optional feature** that you may wish to enable.
+
+The Facebook bridge can create a Matrix community for you, which would contain all your chats and contacts.
+
+For this to work, the bridge's bot needs to have permissions to create communities (also referred to as groups).
+Since the bot is a non-admin user, you need to enable such group-creation for non-privileged users in [Synapse's settings](configuring-playbook-synapse.md).
+
+Here's an example configuration:
+
+```yaml
+matrix_synapse_configuration_extension_yaml: |
+  enable_group_creation: true
+  group_creation_prefix: "unofficial/"
+
+matrix_mautrix_facebook_configuration_extension_yaml: |
+  bridge:
+    community_template: "unofficial/facebook_{localpart}={server}"
+```
+
+Once the bridge is restarted, it would create a community and invite you to it. You need to accept the community invitation manually.
+If you don't see all your contacts, you may wish to send a `sync` message to the bot.
+
+
 ## Troubleshooting
 
 ### Facebook rejecting login attempts and forcing you to change password