Add warn about requirements.txt file to "requirements without setup.py" section of readme

[hramezani]

Resolves #744.

Changelog-friendly one-liner: Add warn about requirements.txt file to "requirements without setup.py" section of readme.

Contributor checklist

• Provided the tests for the changes.
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[atugushev]

Hello @tysonclugg,

Sorry for bothering you. I've requested a review from you since you are the author of the changed paragraph. Could you please review it when you have time? Thanks!

[codecov]

Codecov Report

Merging #959 into master will not change coverage.
The diff coverage is n/a.

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  Coverage    99.1%   99.1%           
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  Files          34      34           
  Lines        2358    2358           
  Branches      305     305           
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  Hits         2337    2337           
  Misses         11      11           
  Partials       10      10

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[hramezani]

Isn't it ready to merge?

[atugushev]

LGTM, but I'm not a native English speaker, so better wait for approvement from another member.

[tysonclugg]

The warning is reasonable, but it applies equally if building requirements.txt from either setup.py or requirements.in. The best solution may be to include a similar warning in a opening statement about what pip-sync and other tools are supposed to achieve, rather than repeating the same warning in multiple sections.

[hramezani]

@tysonclugg Thanks,
@atugushev I moved it as a note to the top of the readme file.

[atugushev]

Markup looks broken, see the how it's rendering:

---

Besides, I think the note should be added to the "Example usage for pip-compile" section. Probably, better to emphasize that the issue with the existing requirements.txt causes only if you start from scratch. I would suggest:

Note: ensure you don't have requirements.txt if you compile setup.py or requirements.in from scratch, otherwise, it might interfere.

[atugushev]

@tysonclugg good point! Thanks :)

[hramezani]

@atugushev it's done.

[atugushev]

Thanks!

[atugushev]

@tysonclugg and @mbeacom, thanks for reviewing this!