Backport changes from #497 and #506 to v0.32 docs

[penelopeysm]

This PR makes some small modifications to the backport-v0.32 branch to make sure it is 100% compatible with the changes in #497.

Specifically, it:

• switches to a single env
• un-gitignores Manifest
• gitignores tmp.gif files
• updates README (cf #506)

[github-actions[bot]]

Preview the changes: https://turinglang.org/docs/pr-previews/507 Please avoid using the search feature and navigation bar in PR previews!

[shravanngoswamii]

Looks good to me!