Fix sed issue on OSX

[embano1]

On OSX sed throws an error if you do not specify a file extension when
-i is given. Fixing the docs to address this on OSX.

Error:

sed: 1: "deploy/operator.yaml": extra characters at the end of d command

From man sed on OSX:

-i extension
             Edit files in-place, saving backups with the specified
	     extension.  If a zero-length extension is given, no backup
	     will be saved.  It is not recommended to give a
	                  zero-length extension when in-place editing
			  files, as you risk corruption or partial
			  content in situations where disk space is
			  exhausted, etc.

[openshift-ci-robot]

Hi @embano1. Thanks for your PR.

I'm waiting for a operator-framework member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[estroz]

LGTM after wording changes.

[estroz]

LGTM. Thanks @embano1!