Update README.md

[janasangeetha]

Updated Docker image hyperlink.

[nikelite]

Hi, TFX contributors,

Sorry for the late responses on the PRs in the TFX repository. The TFX project had been coupled with internal TFX implementations, but we recently decoupled this and updated the CI process to GitHub Actions. So, we can now easily merge external contributions into the main TFX branches.

If you are still interested in merging your PR to the main TFX branch, please update it with the latest version of the TFX repository and run the GitHub Actions tests. If the tests pass with the default version of the TFX libraries, TFX committers will approve and merge your PR. Thanks!