Update the datadog krew plugin installation instructions

[L3n41c]

What does this PR do?

Update the datadog krew plugin installation instructions.

Motivation

We’ve opened a PR to add the datadog plugin into the krew index: kubernetes-sigs/krew-index#727

Additional Notes

Anything else we should know when reviewing?

[codecov-commenter]

Codecov Report

Merging #126 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #126   +/-   ##
=======================================
  Coverage   58.21%   58.21%           
=======================================
  Files          31       31           
  Lines        4353     4353           
=======================================
  Hits         2534     2534           
  Misses       1630     1630           
  Partials      189      189           

Flag	Coverage Δ
#unittests	58.21% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9c71245...e0fa1b6. Read the comment docs.

[ahmed-mez]

👏

[L3n41c]

The datadog plugin is now available via the krew index:

lenaic.huard@COMP11791:~ $ kubectl krew search datadog

lenaic.huard@COMP11791:~ $ kubectl krew update
Updated the local copy of plugin index.
  New plugins available:
    * datadog

lenaic.huard@COMP11791:~ $ kubectl krew search datadog
NAME     DESCRIPTION                  INSTALLED
datadog  Manage the Datadog Operator  yes