Create a dedicated development & release guide

[thomashoneyman]

As discussed in #218, I think we ought to split out the development instructions for Try PureScript from the main README, and we should expand those instructions to include cutting new releases of the project.

The development instructions should cover what they already do: how to set up the local server, how to set up the local client, and how to update the packages and package set.

The release instructions could include things not currently described, including:

• Updating the hardcoded tag used for examples
• How to check that the externs for an upgraded package set don't overwhelm the server
• How to run a deployment

and ideally this could be aggregated in checklist form, so someone who wants to make a release can move step-by-step through the instructions from a fresh clone of the repository.

[JordanMartinez]

I think the only thing not described in the current RELEASE.md file are:

• How to check that the externs for an upgraded package set don't overwhelm the server
• How to run a deployment