Add documenation about setting resource limits on a Task step

[kscherer]

Changes

For our use case we needed a way to limit the number of steps that run simultaneously on a worker node. I tried using limit ranges but when used with sidecars it doubles the resource usage. Thanks to #3756 I learned about this method and decided a doc update could save others the trouble.

/kind documentation

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices
• Release notes block has been filled in or deleted (only if no user facing changes)

See the contribution guide for more details.

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.

Reviewer Notes

If API changes are included, additive changes must be approved by at least two OWNERS and backwards incompatible changes must be approved by more than 50% of the OWNERS, and they must first be added in a backwards compatible way.

NONE

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Konrad Scherer (d976d41)

[tekton-robot]

Hi @kscherer. Thanks for your PR.

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/ok-to-test

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbwsg

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[pritidesai]

NIT: please add this section to TOC on the top of the page.

[pritidesai]

Thank you @kscherer for your contributions 🙏

/lgtm

[bobcatfish]

nice!!! i was actually just looking for docs on this, thanks @kscherer !