docs: contributing guide (#278)

Author: saitonakamura

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing guide
+
+## Prerequisites
+
+* modern version of node
+* yarn classic, https://classic.yarnpkg.com/en/docs/install
+
+## Setup
+
+* Run `yarn` in repo root
+* Run `yarn` in `examples` folder
+
+## Run locally
+
+* Run `yarn dev` to be able to to run examples
+
+## PR checklist
+
+### Run unit tests 
+
+* Run `yarn test`
+
+### Run linter
+
+* Run `yarn lint`
+
+### Test examples locally
+
+Using real device is recommended, otherwise you can use https://github.com/meta-quest/immersive-web-emulator/.
+See [Run locally](#run-locally)