docs: relicense all contributions under Apache 2.0 + LLVM exceptions

[favonia]

@symgryph @JvdMaat I opened this PR so that you can more explicitly approve the relicensing under Apache 2.0 with LLVM exceptions. (The original PR #952 was merged and you can no longer approve it.) Please take your time to approve this PR---I am not in a hurry after just releasing 1.15.0.

---

@symgryph By the way, I plan to investigate how ta create packages for major platforms soon. It will certainly involve packaging the systemd files.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.82%. Comparing base (864be42) to head (b2ff211).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #962   +/-   ##
=======================================
  Coverage   95.82%   95.82%           
=======================================
  Files          62       62           
  Lines        2874     2874           
=======================================
  Hits         2754     2754           
  Misses        108      108           
  Partials       12       12           

Flag	Coverage Δ
unittests	95.82% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.