Update README.md

[llwp]

the capitalization of the build.md file affects whether github serves the file ... the file may have been lowercase at one point - right now it is capitals. this fixes the caps reference so the link is not broken any longer.

[github-actions]

CLA Assistant Lite bot:
Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

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_{You can retrigger this bot by commenting recheck in this Pull Request}

[Cuperino]

Hi @llwp, for your signature to be machine readable it needs to go in this JSON file: https://github.com/Cuperino/Signatures/blob/main/cla-v1.json . The signature will be added there automatically for you. All you must to do is type

I have read the CLA Document and I hereby sign the CLA

in a single line comment on this pull request.

[Cuperino]

@llwp Please type I have read the CLA Document and I hereby sign the CLA in a comment to this pull request, to proceed with merging your change. I recognize your intent, but the CLA has not yet been properly signed.