Documentation update

[lucasreed]

• Removing helm 2 from roadmap since it is implemented
• adding proper CI link to CircleCI badge

[codecov]

Codecov Report

Merging #43 into master will not change coverage.
The diff coverage is 60.00%.

@@           Coverage Diff           @@
##           master      #43   +/-   ##
=======================================
  Coverage   76.41%   76.41%           
=======================================
  Files           5        5           
  Lines         229      229           
=======================================
  Hits          175      175           
  Misses         39       39           
  Partials       15       15           

Impacted Files	Coverage Δ
pkg/helm/helm.go	68.88% <0.00%> (ø)
pkg/api/versions.go	100.00% <100.00%> (ø)

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