Add docs on how to re-enable Keyring

[NiklasRosenstein]

The README outlines how to disable keyring globally using python -m keyring --disable. But it doesn't explain what happens in the background with this command and how to re-enable it. The docs include some note about this, for example

You can re-enable keyring by running python -m keyring diagnose to find the Keyring config file and updating the backend or removing the entire file.

[jaraco]

Sounds good. Would you be interested in drafting the change?

[ankitaa06]

Where can I find the solution for this?

[NiklasRosenstein]

Where can I find the solution for this?

It's right there in the block quote of the initial comment. :) I.e. find the config file and update it.