Add install directions.

CONTRIBUTING.md

@@ -74,6 +74,14 @@ and a few modules:
 3. Run `npm install`
 4. Run `npm test` to see whether your tests pass or fail.
 
+## Building / Installing
+
+You can build and install a concatenated and minified version of iD with the command `make install`.
+Node.js is required for this.
+
+By default iD will be built to the `build` directory, but you can move it elsewhere or specify the
+build location with `make install install_root=/path/to/install`.
+
 ## Licensing
 
 iD is under the [WTFPL](http://www.wtfpl.net/). Some of the libraries it uses

README.md

@@ -30,6 +30,9 @@ Come on in, the water's lovely. More help? Ping RichardF, tmcw, or jfire on IRC
 (`irc.oftc.net`, in `#osm-dev` or `#osm`), on the OSM mailing lists or at
 richard@systemeD.net.
 
+For guidance on building a packaged version, running tests, and contributing to
+development, see [CONTRIBUTING.md](CONTRIBUTING.md).
+
 ## License
 
 iD is available under the [WTFPL](http://sam.zoy.org/wtfpl/), though obviously, if you want to dual-license