update contributing md
Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this [failed invocation](https://github.com/tensorflow/tensorflow/pull/62074/checks?check_run_id=17532730903) of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request. Please don't use "add file"/"update file"/"fix file"/etc. commit messages. These are hard to reason about when looking at the history of the file/repository. Instead, please write explanatory git commit messages.

The commit message is also the title of the PR if the PR has only one commit. It is thus twice important to have commit messages that are relevant, as PRs would be easier to understand and easier to analyze in search results.

For how to write good quality git commit messages, please consult https://cbea.ms/git-commit/  Also, please sign CLA and squash all commits in a single one, it does not make sense to have 3 different commits for editing a single file I think I have squashed all the commits successfully. please check. Sorry for my mistakes, I'm just learning and trying my best.
The contributing md is not up to date. tensorflow/tensorflow:devel and tensorflow/tensorflow:devel-gpu docker file tags are no longer supported. also this links does not point to the correct files or page. I have updated a small link and intend to update the instructions so that its more clear and concise.