[docs] write up a guide for GitHub builds (#23214)

# Why

The first iteration of GitHub builds are releasing soon, so it would be
great to document how to use it.

# How

- I wrote up a short

[docs] write up a guide for GitHub builds (#23214)

# Why

The first iteration of GitHub builds are releasing soon, so it would be
great to document how to use it.

# How

- I wrote up a short guide detailing how to set up a project and
repository for building from GitHub.
- I also updated the programmatic access docs to de-specify the
availability of bot users since all accounts can use them now

# Test Plan

Run the docs locally and visit
http://localhost:3002/build/building-from-github/ to view the new guide

# Checklist

<!--
Please check the appropriate items below if they apply to your diff.
This is required for changes to Expo modules.
-->

- [ ] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
- [ ] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [ ] This diff will work correctly for `npx expo prebuild` & EAS Build
(eg: updated a module plugin).

---------

Co-authored-by: Jon Samp <[email protected]>
Co-authored-by: Aman Mittal <[email protected]>

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