docs: refresh documentation store

[jackfrancis]

Reason for Change:

This PR is the result of a focused refresh of all (well, most) documentation in the repo. It should be reviewed for sanity in terms of truthful corrections to narrative, and amendments/standardizations to various references, and some light grammar (intended) improvements.

Issue Fixed:

Fixes #3170

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3177 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3177   +/-   ##
=======================================
  Coverage   71.23%   71.24%           
=======================================
  Files         147      147           
  Lines       25745    25753    +8     
=======================================
+ Hits        18340    18348    +8     
  Misses       6268     6268           
  Partials     1137     1137           

Impacted Files	Coverage Δ
cmd/addpool.go	18.91% <ø> (ø)
cmd/rotate_certs.go	67.93% <ø> (ø)
cmd/scale.go	12.39% <ø> (ø)
cmd/upgrade.go	44.56% <ø> (ø)
cmd/version.go	100.00% <ø> (ø)
cmd/deploy.go	62.61% <100.00%> (ø)
cmd/generate.go	50.38% <100.00%> (ø)
pkg/engine/templates_generated.go	38.36% <0.00%> (ø)
pkg/api/vlabs/validate.go	80.19% <0.00%> (+0.03%)	⬆️
pkg/api/defaults-kubelet.go	96.66% <0.00%> (+0.11%)	⬆️

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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