Spelling fixes in our doc

[skaegi]

Found using mdspell -a -n --en-us "**/*.md". At some point we might want to have a built in ignore dictionary to avoid false positives.

Changes

Just minor spelling fixes (I assumed en-us spelling for consistency)

Submitter Checklist

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• Includes tests (if functionality changed/added)
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Double check this list of stuff that's easy to miss:

• If you are adding a new binary/image to the cmd dir, please update
  the release Task to build and release this image.

[ghost]

I take offence at this behaviour.

/approve
/lgtm

[tekton-robot]

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[ghost]

/test pull-tekton-pipeline-build-tests

[skaegi]

/retest

[skaegi]

It's behaviour up here in the north too but... must be consistent. ;)