Prettier docs (#28)

To get a cleaner diff when adding v2.3.1.1 docs, this is a preliminary
PR applying `prettier` formatting of all relevant files.

README.md

@@ -32,6 +32,15 @@ The spec is currently at version 2.2.0.
 
 The documentation is currently generated by Sphinx. It can be generated locally with:
 
-	docker run --rm -v $PWD:/opt -w /opt -e USER_ID=$UID ddidier/sphinx-doc:2.2.1-1 sphinx-build -b html source build
+    docker run --rm -v $PWD:/opt -w /opt -e USER_ID=$UID ddidier/sphinx-doc:2.2.1-1 sphinx-build -b html source build
 
 The generated documentation is then rooted in `build/index.html`.
+
+## Code formatting
+
+The code is formatted with Prettier. To format the code, run:
+
+```
+npm install -g prettier
+prettier . --write --bracket-same-line
+```