Add lang#puppet layer doc

[wsdjeg]

PR Prelude

Thank you for working on SpaceVim! :)

Please complete these steps and check these boxes before filing your PR:

• I have read and understood SpaceVim's CONTRIBUTING document.
• I have read and understood SpaceVim's CODE_OF_CONDUCT document.
• I have updated the Following-HEAD page for this PR.
• I understand my PR may be closed if it becomes obvious I didn't actually perform all of these steps.

Why this change is necessary and useful?

close #2040

[codecov]

Codecov Report

Merging #2198 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #2198   +/-   ##
=======================================
  Coverage   25.99%   25.99%           
=======================================
  Files         270      270           
  Lines       13647    13647           
=======================================
  Hits         3547     3547           
  Misses      10100    10100

[wsdjeg]