README: link to the list of available plugins

[ahmetb]

ref: #303

/hold
until kubernetes-sigs/krew-index#202 merged.

[codecov-io]

Codecov Report

Merging #304 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #304   +/-   ##
=======================================
  Coverage   55.66%   55.66%           
=======================================
  Files          19       19           
  Lines         918      918           
=======================================
  Hits          511      511           
  Misses        355      355           
  Partials       52       52

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[corneliusweig]

/hold cancel
/retitle README: link to the list of available plugins

[corneliusweig]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahmetb, corneliusweig

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