packaging - remove all files from OBS checkout before copying

to get rid of obsoleted files
Merge pull request #387 from lslezak/package_cleanup

packaging - remove all files from OBS checkout before copying
README.md: Make "Module Metadata" a level 2 heading

It doesn't really belong to the "Usage" section. This change also puts
the "Module Metadata" section to the same level as "New YaST Module
Structure", which is kind of similar (both are essentially references).
README.md: Reorder command descriptions alphabetically
README.md: Add stubs for "yk build" and "yk submit"

Content will be filled-in later.
README.md: Add "Contents" section
Merge pull request #388 from yast/readme-structural-improvements

[Review] Request from '' @ 'yast/ycp-killer/readme-structural-improvements'
README.md: Update "yk help" output to match reality
README.md: Improve the "Usage" section

  * Remove redundant sections from the intro text, move everything into
    one place.

  * Change terminology: s/subcommand/command/

  * Use four spaces instead of ``` to delimit "yk help" output. It is
    more readable in plaintext.

  * Other small improvements.
README.md: Remove examples of executed commands

I don't think they are very helpful as they all look more or less the
same. They also create maintenance burden as they need to be updated
when command output changes.
Merge pull request #389 from yast/readme-usage-improvements

[Review] Request from '' @ 'yast/ycp-killer/readme-usage-improvements'