README.md: Describe more config variables, cleanup

Added some documentation of environment variables to README.md,
specifically WORK_DIR and DEPLOY_DIR.  Explicitly did not include
SCRIPT_DIR at this time because that appears to require some small work
before it can be changed.

Took the chance for some other syntax cleanups while I was at it, mostly
breaking long lines and inserting whitespace where some Markdown parsers
require it.
1 file changed