Add using kubectl to install the CRDs

[mattj-io]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/component generator
/component kudoctl
/component operator
/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind feature
/kind enhancement
/kind infrastructure
/kind kep

What this PR does / why we need it:

Update docs to show installing CRDs using kubectl instead of the Makefile provided function

Which issue(s) this PR fixes:

Fixes

Special notes for your reviewer:

This was suggested in #209, and simplifies understanding of what is being installed without the user having to dig into the Makefile

Does this PR introduce a user-facing change?:

NONE