Docs: github-mode: Hint at different env var names (Thinkmill#1356)

Author: tordans

docs/src/content/pages/github-mode.mdoc

@@ -89,7 +89,7 @@ Behind the scenes, some environment variables were generated in a `.env` file on
 KEYSTATIC_GITHUB_CLIENT_ID=...
 KEYSTATIC_GITHUB_CLIENT_SECRET=...
 KEYSTATIC_SECRET=...
-NEXT_PUBLIC_KEYSTATIC_GITHUB_APP_SLUG=...
+NEXT_PUBLIC_KEYSTATIC_GITHUB_APP_SLUG=... # for Next.JS or `PUBLIC_KEYSTATIC_GITHUB_APP_SLUG` for Astro
 ```
 
 These variables are used to authenticate users with GitHub, based on their access to the GitHub repo in question.
@@ -131,4 +131,4 @@ This segment of the [Keystatic Mini-Course on YouTube](https://www.youtube.com/p
 
 {% embed
    mediaType="video"
-   embedCode="<iframe src=\"https://www.youtube.com/embed/BAnfePGzkbg?si=mDDK52Nlhg4v1v9x\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen></iframe>" /%}
+   embedCode="<iframe src=\"https://www.youtube.com/embed/BAnfePGzkbg?si=mDDK52Nlhg4v1v9x\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen></iframe>" /%}