update readmes for bcftools, htslib, and samtools

[Kincekara]

I updated image specific and main readme files for the new bcftools, samtools and htslib 1.20.c.

Pull Request (PR) checklist:

• [ ] Include a description of what is in this pull request in this message.
• [ ] The dockerfile successfully builds to a test target for the user creating the PR. (i.e. docker build --tag samtools:1.15test --target test docker-builds/samtools/1.15 )
• [ ] Directory structure as name of the tool in lower case with special characters removed with a subdirectory of the version number (i.e. spades/3.12.0/Dockerfile)
  • [ ] (optional) All test files are located in same directory as the Dockerfile (i.e. shigatyper/2.0.1/test.sh)
• [x] Create a simple container-specific README.md in the same directory as the Dockerfile (i.e. spades/3.12.0/README.md)
  • [ ] If this README is longer than 30 lines, there is an explanation as to why more detail was needed
• [ ] Dockerfile includes the recommended LABELS
• [x] Main README.md has been updated to include the tool and/or version of the dockerfile(s) in this PR
• [x] Program_Licenses.md contains the tool(s) used in this PR and has been updated for any missing

[erinyoung]

I have no changes to request, so I'm going to merge this.

It doesn't look like there's anything to deploy.

[Kincekara]

Thank you!