Tau - update readme

Now includes basic instructions on how to run in prod and dev mode

(not that this currently makes lots of sense outside of the context of Sonic Pi's app structure - but likely will soon)

Author: samaaron

app/server/beam/tau/README.md

@@ -3,4 +3,53 @@
 Erlang/Elixir IO Server with C++ NIFs for MIDI and Link plus support for
 future Rust NIFs.
 
+# Development mode
+
+To manually start the Tau server in development mode:
+
+1. Set the `MIX_ENV` environment variable to `dev`
+2. Run the `setup.dev` mix action
+3. Start mix with the `--no-halt` flag.
+
+```batchfile
+rem Windows
+set MIX_ENV=dev
+mix setup.dev
+mix run --no-halt
+```
+
+```shell
+# macOS/Linux
+MIX_ENV=dev
+mix setup.dev
+mix run --no-halt
+```
+
+Note, you will need to connect the browser to localhost on the port which is printed to the log files.
+
+Also, note, that unless you compile and provide the shared libraries for the MIDI and Link NIFs, this functionality will not be available.
+
+
+# Production mode
+
+When Tau is packaged into a Sonic Pi release, it is first turned into a mix release which is then started with `MIX_ENV=prod`. You can manually achieve this with the following:
+
+
+```batchfile
+rem Windows Command Prompt
+set MIX_ENV=prod
+mix tau.release
+_build\prod\rel\tau\bin\tau start > NUL 2>&1
+```
+
+```shell
+# macOS/Linux Terminal Prompt
+MIX_ENV=dev
+mix tau.release
+_build/prod/rel/tau/bin/tau start > /dev/null 2>&1
+```
+
+
+
+