Merge pull request #1568 from tyleretters/update-readme

update readme.md

readme.md

@@ -11,10 +11,12 @@ norns is many sound instruments. it connects to grids, MIDI, and other objects.
 git clone https://github.com/monome/norns.git
 cd norns
 git submodule update --init --recursive
-./waf configure
-./waf
+./waf configure --release
+./waf build --release
 ```
 
+(NB: the `--release` flag creates builds specifically for armv8/cortex-a53 instruction set, meaning optimized for rpi3 and compatible with rpi4. It also enables aggressive compiler optimizations. Omit flag if you need debug symbols or to build for a different architecture. It does need to supplied to both configuration and build steps.)
+
 ## documentation
 - [user docs](https://monome.org/docs/norns)
 - [API docs](https://monome.org/docs/norns/api)