Doc: improve getting started guide

Removed site configuration section, which is already covered by the
installtion chapter.

And fixed a typo.
Doc: explain text editor foreground requirement
rose edit: guarantee cwd for macros.

This change guarantees that a macro or upgrade macro
runs with a current working directory of the
relevant configuration directory within rose edit.
Merge pull request #1114 from benfitzpatrick/rose-edit.app-dir-cwd-for-macro

rose edit: guarantee cwd for macros.
Merge pull request #1108 from matthewrmshin/doc

Doc: improve getting started guide