Update "go install" instructions

[xuhdev]

I got the following error when following the original instructions:

go install: version is required when current directory is not in a module
        Try 'go install github.com/google/ko@latest' to install the latest version

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[codecov-commenter]

Codecov Report

Merging #377 (ffae306) into main (ee23538) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #377   +/-   ##
=======================================
  Coverage   44.04%   44.04%           
=======================================
  Files          33       33           
  Lines        1605     1605           
=======================================
  Hits          707      707           
  Misses        769      769           
  Partials      129      129           

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[imjasonh]

Sorry for the long delay on this PR. We had an issue with kind e2e tests that was resolved in #184 -- if you rebase you should pick it up, and tests should pass, and we can merge this. Otherwise I'd be happy to make the change myself.