docs: README install quick start names the Forgejo channel (RIG_HOST)

README.md

@@ -19,6 +19,9 @@ takes arguments, does its work, and stores no credential, ever.
 curl -fsSL https://raw.githubusercontent.com/heavy-duty/rig/main/install.sh | RIG_REF=main bash
 # the latest release:
 curl -fsSL https://raw.githubusercontent.com/heavy-duty/rig/main/install.sh | bash
+# either channel from the Forgejo mirror (RIG_HOST picks the forge; #111):
+curl -fsSL https://forgejo.heavyduty.builders/heavy-duty/rig/raw/branch/main/install.sh \
+  | RIG_HOST=https://forgejo.heavyduty.builders bash
 ```
 
 This README tracks `main`, so the quick start installs that same development
@@ -37,6 +40,11 @@ curl -fsSL .../install.sh | RIG_REF=main bash      # the development tree
 A tag outranks a branch of the same name (the pin must win); anything that
 is not a tag falls back to `refs/heads/<ref>`.
 
+`RIG_HOST` picks the forge the channel reads — `https://github.com` by
+default (#111) — and it is chosen independently of the URL the script itself
+came from, so installing *from* the Forgejo mirror means naming the mirror
+twice, as the quick start's third line does.
+
 The layout, under the install root (`~/.local/share/rig`):
 
 ```

changelog.d/131.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- The README's install quick start documents the Forgejo channel — `RIG_HOST` shipped in #111 but was documented nowhere (#131)