Restructure of the Getting Started section

[phschimm]

• Simplified master.asciidoc structure (by introducing master-contributing.asciidoc in /general)
• Renamed some files:
  • master-release-notes.asciidoc (to better comply with the guidelines)
  • oss-compliance.asciidoc (shorter, better to identify)
• Moved introduction sections to the getting-started repo (see PR#19)

[jambulud]

Could you solve the merge conflict?

<<<<<<< getting_started_rework
[submodule "getting-started.wiki"]
	path = getting-started.wiki
	url = https://github.com/devonfw/getting-started.wiki.git
=======
[submodule "cobigen.wiki"]
	path = cobigen.wiki
	url = https://github.com/devonfw/cobigen.wiki.git
>>>>>>> master

It's an easy to solve conflict because both submodules should be on devonfw-guide