docs: add note for signing jwt with symmetric keys

[yaskoo]

No description provided.

[CLAassistant]

All committers have signed the CLA.

[aeneasr]

Thank you, this looks great! It looks like the CLA bot is not properly detecting your signature. To fix this, try the following:

$ git commit  --amend --author="Author Name <email@address.com>"

Ensure that Author Name is replaced with your GitHub username (e.g. aeneasr) and that the email address is replaced with the email address you have set up in GitHub (e.g. 3372410+aeneasr@users.noreply.github.com):

$ git commit  --amend --author="aeneasr <3372410+aeneasr@users.noreply.github.com>"

Once that is done, you can force-push your changes (make sure to push to the correct remote and branch!):

$ git push --force <remote> HEAD:<branch>

[aeneasr]

👍