Add missing compresslevel parameter on docs

[junah201]

Summary

The compresslevel parameter was added in #1128.
But, it was not added to the document, so I added an explanation on docs.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Kludex]

Thanks @junah201