Docs link update

[shivam-V8]

The backlink in https://docs.bittensor.com/ does not have an active Github repo. text prompting subnet: As this project is no longer maintained, we need to change it to (https://github.com/opentensor/prompting), which is an active repository.

[rajkaramchedu]

@shivam-V8, thanks for this. I am rewriting the code walkthrough doc as the repo has changed significantly. For now I am keeping these broken links as they are in the code walkthrough doc, but fixed elsewhere.