docs: add auth token troubleshooting

[saurabhhhcodes]

Summary

• add a concise troubleshooting section for empty/unresolved authorization headers
• document env var checks, .env location expectations, and bash/zsh plus PowerShell token examples

Fixes #9

Validation

• git diff --check

GSSoC labels requested

Please add/keep gssoc and the required difficulty/type scoring labels if this is accepted.

[saurabhhhcodes]

Hi maintainer, this docs PR is still ready and mergeable. It adds a short troubleshooting section around auth token resolution without changing runtime behavior, so it should be a lightweight review. If it fits your queue, please also copy the appropriate GSSoC labels onto the PR when reviewing.