Clean-up and replace Licensing chapter

[egpbos]

• Add a section to Best Practices.
  • NLeSC-internal note: refer to the PMP, "we preferably use Apache v2".
• Remove the chapter PR
• Afterwards: check for broken links (globally! the PR link checker only checks changed files...)

[egpbos]

Because of the NLeSC-internal reference, this should wait until #394 is merged.

[egpbos]

#394 is merged, this issue is unblocked.