Support both binary & source install, improved README, fixed systemd service etc.

README.md

@@ -1,2 +1,26 @@
-# matrixmailer
+# Ansible role for matrixmailer
+This role will install [matrixmailer](https://gitea.a-0.me/philip/matrixmailer) - either with pre-built binaries, or from source code directly on your system. It also sets up a systemd service and enables it.
 
+# Supported operating systems
+This playbook currently only supports debian systems. To suggest other platforms or contribute, feel free to join [#matrixmailer:a-0.me](matrix:r/matrixmailer:a-0.me).
+
+Despite higher system performance requirements, I recommend self-building the binary as the cross compiling is still in an experimental stage.
+
+# Configuration
+See example playbooks for configuration samples.
+
+Required variables:
+- `matrixmailer_version`: Pinned version of matrixmailer to install, e.g. "0.1.0"
+- `matrixmailer_build`: Either "from_source" if you want to build it yourself, or the build target for prebuilt binaries, like "x86_64-unknown-linux-musl"
+- `matrixmailer_config`: Yaml content of the configuration file. You may want to consider importing it from a file rather than putting the file content directly into the playbook.
+
+Optional variables:
+- `matrixmailer_git_repo`: Only used when self-building the binary. Allows you to specify any URL a matrixmailer git repository can be pulled from.
+
+# System requirements
+matrixmailer itself is very lightweight. However, self-building matrixmailer is only recommended on systems with
+- at least one "powerful" or two CPU cores, and
+- at least 2GB memory.
+
+# Disclaimer
+Please be aware that this ansible role, as well as matrixmailer itself, are under active development. Be careful using it on production systems.