fix: Mention node on readme, drop python requirement

Makefile

@@ -17,7 +17,7 @@ clean:
 	rm -rf *.img *.model *.manifest snaps
 
 %.model: boards/%.yaml # sign a model file
-	cat definition.yaml $< | python -c "import sys, yaml, json; json.dump(yaml.load(sys.stdin), sys.stdout, indent=2)" | sed "s|TIMESTAMP|$(shell date -Iseconds --utc)|g" | snap sign -k "$(USER_KEY)" > $@
+	cat definition.yaml $< | node json2yaml.js | sed "s|TIMESTAMP|$(shell date -Iseconds --utc)|g" | snap sign -k "$(USER_KEY)" > $@
 snaps/%: deps/%.yaml
 	node build-tool.js --env $(ENV) --channel $(CHANNEL) --board $*
 .cloud-init.yaml: $(ENV).cloud-init.yaml

README.md

@@ -10,12 +10,14 @@ Everything subject to change, including number of bugs (hopefully to zero ;)
 
 ## System Requirements
 
-To build an image you need to have at least Ubuntu 16.04 on your machine and the following packages installed: `ubuntu-image snapd`
+To build an image you need to have at least Ubuntu 16.04 on your machine and the following packages installed: `ubuntu-image snapd nodejs`
 
 Additionally at least 1 GB of free disk space is required
 
 For virtual device testing you also need `qemu-kvm`
 
+Additionally some npm packages are required, run `npm i` to install them
+
 ## Other Requirements
 
  - Ubuntu One account

json2yaml.js

@@ -0,0 +1,9 @@
+'use strict'
+
+const yaml = require('js-yaml')
+let d = []
+
+process.stdin.on('data', data => d.push(data))
+process.stdin.on('end', () => {
+  console.log(JSON.stringify(yaml.safeLoad(Buffer.concat(d)), null, 2))
+})