improve "Building a development environment"

[Reimar Bauer]

For starting the first listed idea to set up the environment is an advanced option while the second is extremly simple.

The documentation should take fokus on new contributor. The first method should be moved to the wiki.

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[Reimar Bauer]

Merged in ReimarBauer/mss/i526 (pull request #774)

explained how to create a local build, synced meta.yaml, fixes #524, #526

→ <<cset ccbfefb085e5>>