updated mail to build
Merge pull request #395 from lslezak/mail_buildfix

updated "mail" to build
README.md: Improve the "Module Metadata" section

The goals were to improve the flow and clarity, sync the terminology
with the "Usage" section and make the formatting more consistent (e.g.
use 80 chars fully).
Merge pull request #396 from yast/readme-module-metadata

README.md: Improve the "Module Metadata" section