docs: add development builds install page

Move the container image and binary download details from the README
into a dedicated documentation page at setup/install/main. This gives
development builds a proper home in the docs site alongside the other
install methods. The README now links to the docs page instead.

README.md

@@ -67,22 +67,9 @@ For NixOS users, a module is available in [`nix/`](./nix/).
 
 ## Builds from `main`
 
-Each push to `main` automatically builds container images and binaries.
-These track the latest development state and are not versioned releases.
-
-**Container images** (multi-arch: amd64, arm64):
-
-- `ghcr.io/juanfont/headscale:main-<sha>`
-- `docker.io/headscale/headscale:main-<sha>`
-
-**Binary downloads** (latest successful build via [nightly.link](https://nightly.link/juanfont/headscale/workflows/container-main/main)):
-
-| OS    | Arch  | Download                                                                                                                   |
-| ----- | ----- | -------------------------------------------------------------------------------------------------------------------------- |
-| Linux | amd64 | [headscale-linux-amd64](https://nightly.link/juanfont/headscale/workflows/container-main/main/headscale-linux-amd64.zip)   |
-| Linux | arm64 | [headscale-linux-arm64](https://nightly.link/juanfont/headscale/workflows/container-main/main/headscale-linux-arm64.zip)   |
-| macOS | amd64 | [headscale-darwin-amd64](https://nightly.link/juanfont/headscale/workflows/container-main/main/headscale-darwin-amd64.zip) |
-| macOS | arm64 | [headscale-darwin-arm64](https://nightly.link/juanfont/headscale/workflows/container-main/main/headscale-darwin-arm64.zip) |
+Development builds from the `main` branch are available as container images and
+binaries. See the [development builds](https://headscale.net/stable/setup/install/main/)
+documentation for details.
 
 ## Talks