Update README.md

[CecileRobertMichon]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

If applicable:

• documentation
• unit tests
• tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

[codecov]

Codecov Report

Merging #2797 into master will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2797      +/-   ##
==========================================
- Coverage   46.93%   46.82%   -0.12%     
==========================================
  Files          86       86              
  Lines       12786    12774      -12     
==========================================
- Hits         6001     5981      -20     
- Misses       6231     6249      +18     
+ Partials      554      544      -10

Impacted Files	Coverage Δ
pkg/helpers/helpers.go	9.09% <0%> (-5.2%)	⬇️
pkg/api/vlabs/validate.go	40.73% <0%> (-2.5%)	⬇️
pkg/api/convertertoagentpoolonlyapi.go	28.11% <0%> (-0.37%)	⬇️
pkg/acsengine/engine.go	62.72% <0%> (-0.11%)	⬇️
cmd/upgrade.go	0% <0%> (ø)	⬆️
cmd/scale.go	0% <0%> (ø)	⬆️
pkg/api/convertertoapi.go	56.62% <0%> (+0.1%)	⬆️
cmd/deploy.go	23.95% <0%> (+0.14%)	⬆️

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[CecileRobertMichon]

@jackfrancis any acs-engine features you'd like to see mentioned here?

[jackfrancis]

I think this is fine for now

[jackfrancis]

lgtm