Update installation related docs

CONTRIBUTING.md

@@ -73,18 +73,17 @@ steps:
 ```bash
 git clone https://github.com/<your-github-username>/jupyterlab.git
 cd jupyterlab
-pip install -e . # will take a long time to build everything
+pip install -e .
 npm install
-npm run build:main
+npm run build  # Build the dev mode assets
+jupyter lab build  # Build the app dir assets
 jupyter serverextension enable --py jupyterlab
 ```
 
 Notes:
 
-* At times, it may be necessary to clean your local repo with the command ``git
-clean -fdx``.
-
-* Make sure to do `pip install -e` *before* running `npm install`. Running `npm install` first makes pip stall.
+* At times, it may be necessary to clean your local repo with the command `npm run clean:slate`.  This will clean the repository, and re-install and 
+rebuild.  If using a local install, you will need to re-run `pip install -e .`
 
 * If `pip` gives a `VersionConflict` error, it usually means that the installed
 version of `jupyterlab_launcher` is out of date. Run `pip install --upgrade

README.md

@@ -54,11 +54,17 @@ Note: If installing using `pip install --user`, you must add the user-level
  `bin` directory to your `PATH` environment variable in order to launch
  `jupyter lab`.
 
-Note: If installing from source and not using the
-development installation (`pip install -e .`), you
-must run `jupyter lab build` after the install to
-get a working application directory.
+Note: JupyterLab can be installed from a git checkout using `pip`.  Note
+that you will have to build the application after installing to get the static 
+assets.  `pip` will warn you that the static assets are not included when 
+installing, and it will fail to build a cached wheel if it decides to try 
+and make one.  Example:
 
+```bash
+pip install git+git://github.com/jupyterlab/jupyterlab.git
+jupyter lab build   # Requires nodejs
+jupyter serverextension enable --py jupyterlab --sys-prefix
+```
 
 ### Running