Add login troubleshooting steps to README

[Moses249]

Purpose

This PR adds a "Login Error Troubleshooting" section under "Deploying" in the README. It helps users resolve login issues during deployment by providing steps to log out, log in, and verify their account.

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[ ] Yes
[x] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[ ] Yes
[x] No

Type of change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Documentation content changes
[ ] Other... Please describe:

Code quality checklist

See CONTRIBUTING.md for more details.

• The current tests all pass (python -m pytest).
• I added tests that prove my fix is effective or that my feature works
• I ran python -m pytest --cov to verify 100% coverage of added lines
• I ran python -m mypy to check for type errors
• I either used the pre-commit hooks or ran ruff and black manually on my code.

[pamelafox]

These steps all use the Azure CLI, but this repo uses the Azure Developer CLI, so these steps shouldn't affect success with this repo. If you need to use a different account, you'd need to use "azd auth logout" and "azd auth login".
If there's an issue with azd login, we could ask that team to add a helpful page under the docs, so that we can link all azd templates to it:
https://learn.microsoft.com/en-us/azure/developer/azure-developer-cli/install-azd

[pamelafox]

I'll close this PR since it use the Azure CLI instead of azd CLI, and I haven't heard back from you. If you think the azd documentation could use a debugging section, please file here:
https://github.com/azure/azure-dev