get-started: cheat sheet update (#21806)

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## Description

Edited cheat sheet pdf directly to add the context "." at the end of
docker build example.


https://deploy-preview-21806--docsdocker.netlify.app/get-started/docker_cheatsheet.pdf

## Related issues or tickets

Closes #18575 

## Reviews

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- [ ] Editorial review

Signed-off-by: Craig <[email protected]>

Author: craig-osterhout