README.md: update with some new links, refresh

And remove Darwin from the list, as macOS was already there.

Change-Id: I76bdcad97c926771f44a67140af21f07a8334796
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f