Contributing: Use meson to install development dependencies

CONTRIBUTING.md

@@ -24,7 +24,7 @@ You're welcome to contribute to the [code](#contributing-to-the-code) or to the
 You'll need [NPM](https://www.npmjs.com/) to install the development dependencies:
 
 ```bash
-npm install --save-dev
+meson compile -C builddir dev
 ```
 
 When you're done, commit all your changes. Make one commit per change. The commit message must include which part of the code you worked on. Example:

meson.build

@@ -16,5 +16,10 @@ INSTALL_DIR = get_option('datadir') / 'gnome-shell' / 'extensions' / UUID
 gnome = import('gnome')
 i18n = import('i18n')
 
+npm_exe = find_program('npm')
+if npm_exe.found()
+	run_target('dev', command: [ npm_exe, 'install', '--save-dev' ])
+endif
+
 subdir('src')
 subdir('tests')