Document raspberry pi support

docs/prerequisites.md

@@ -1,6 +1,6 @@
 # Prerequisites
 
-- An x86 server running **CentOS** (7 only for now; [8 is not yet supported](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/300)), **Debian** (9/Stretch+) or **Ubuntu** (16.04+). This playbook doesn't support running on ARM so it won't work on a Raspberry Pi. We only strive to support released stable versions of distributions, not betas or pre-releases. This playbook can take over your whole server or co-exist with other services that you have there.
+- An x86 server running **CentOS** (7 only for now; [8 is not yet supported](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/300)), **Debian** (9/Stretch+) or **Ubuntu** (16.04+). This playbook doesn't support running on ARM ([see](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/299)), however some workarounnd exist for the [Raspberry Pi](raspberry-pi.md). We only strive to support released stable versions of distributions, not betas or pre-releases. This playbook can take over your whole server or co-exist with other services that you have there.
 
 - [Python](https://www.python.org/) being installed on the server. Most distributions install Python by default, but some don't (e.g. Ubuntu 18.04) and require manual installation (something like `apt-get install python`).
 

docs/raspberry-pi.md

@@ -0,0 +1,17 @@
+# Raspberry Pi
+
+The playbook support for Raspberry Pi is now in beta(ish). The problem is that, docker containers are not architecture independent, and most of them are not build for arm. Some roles have been updated, so they built the necessary image on the host. It needs more space, as some build tools need to be present (like Java, for mxisd).
+
+To use these modification there is a variable that needs to be switched to enable this functionality. Add this to your vars.yaml file:
+```
+matrix_raspberry_pi = true
+```
+
+List of roles that builtds the image:
+- synapse
+- coturn
+- mxisd
+- matrix-bridge-mautrix-facebook
+- matrix-bridge-mautrix-hangouts
+
+nginx hopefully works as it has an arm image already.