Clarify FAQ: BYOK works without GitHub Copilot subscription (#336)

* Initial plan

* Update README FAQ to clarify BYOK doesn't require GitHub subscription

Co-authored-by: lossyrob <2320142+lossyrob@users.noreply.github.com>

* Clarify that free tier applies to non-BYOK usage

Co-authored-by: lossyrob <2320142+lossyrob@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: lossyrob <2320142+lossyrob@users.noreply.github.com>

Author: lossyrob

README.md

@@ -55,7 +55,7 @@ The SDK manages the CLI process lifecycle automatically. You can also connect to
 
 ### Do I need a GitHub Copilot subscription to use the SDK?
 
-Yes, a GitHub Copilot subscription is required to use the GitHub Copilot SDK. Refer to the [GitHub Copilot pricing page](https://github.com/features/copilot#pricing). You can use the free tier of the Copilot CLI, which includes limited usage.
+Yes, a GitHub Copilot subscription is required to use the GitHub Copilot SDK, **unless you are using BYOK (Bring Your Own Key)**. With BYOK, you can use the SDK without GitHub authentication by configuring your own API keys from supported LLM providers. For standard usage (non-BYOK), refer to the [GitHub Copilot pricing page](https://github.com/features/copilot#pricing), which includes a free tier with limited usage.
 
 ### How does billing work for SDK usage?