fix: "tesserocr" instead of "tesseract_cli" in usage docs

[Ryfernandes]

The current usage docs have tesseract-cli as an allowed value for ocr_engine, but the error message below from docling-serve indicates that the value tesseract-cli should actually be tesserocr:

Error: "msg":"Input should be 'easyocr', 'ocrmac', 'rapidocr', 'tesserocr' or 'tesseract'","input":"tesseract_cli"

This fix updates the usage docs with this small change, as well a short instruction on installing tesserocr

[mergify]

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[dolfim-ibm]

@Ryfernandes thanks for the fix. to accept this contribution we require all the commits to be properly signed off. More details at https://github.com/docling-project/docling-serve/pull/223/checks?check_run_id=44185455883

Note: we just simplify the sign-off process, if you rebase your branch on the latest main branch you can sign-off with a remediation commit.

[github-actions]

✅ DCO Check Passed

Thanks @Ryfernandes, all your commits are properly signed off. 🎉

[Ryfernandes]

@dolfim-ibm thanks for letting me know! I just rebased with the proper sign-off

[dolfim-ibm]

lgtm