perf: `--depth=1` shallow clone for end users

[agilgur5]

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Summary

Speed up downloads of the script with a more efficient shallow clone

Details

• rather than cloning the entire history of the repo, can do a shallow clone with a depth of 1

  • this should make it more efficient, particularly when there are many commits or many large commits
  • since the history is unused by regular end users, there is no need to fetch/download it

• also add syntax highlighting to the first code block, matching the second one

Notes to Reviewers

• could alternatively do a bare clone to be even more efficient
  • but I thought a shallow clone is a bit less intrusive for now
    • and is reversible, if needed (i.e. a local shallow clone can fetch the rest of the depth)

References

This is largely equivalent to https://github.com/ryanrudolfoba/SteamOS-Waydroid-Installer/pull/198