docs(faq): categorize faq into "how to", "feature request graveyard",…

[bearomorphism]

… and "history"

Why

Now faq page focuses on "how to do XXX", and "feature request graveyard" is about decisions.

Better name suggestions are welcome.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 97.88%. Comparing base (120d514) to head (dd8674b). :warning: Report is 881 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1722      +/-   ##
==========================================
+ Coverage   97.33%   97.88%   +0.55%     
==========================================
  Files          42       60      +18     
  Lines        2104     2605     +501     
==========================================
+ Hits         2048     2550     +502     
+ Misses         56       55       -1     

Flag	Coverage Δ
unittests	97.88% <ø> (+0.55%)	:arrow_up:

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