common/container: remove gconv noextract, add README

noextracting gconv was breaking CI for limine

common/container/README.md

@@ -0,0 +1,9 @@
+## void-packages buildroot containers
+
+These containers are used for CI and should contain everything needed to run xbps-src.
+
+### Updating
+
+To build a new version, kick off a CI run by pushing something to `common/container/` on `master` or using the `Run workflow` button [here](https://github.com/void-linux/void-packages/actions/workflows/container.yaml).
+
+Once this is built, update the version where it is used in `.github/workflows/` (typically in the value of a `container.image` key) to the newly-built tag.

common/container/noextract.conf

@@ -10,4 +10,3 @@ noextract=/usr/share/fish/vendor-completions.d*
 noextract=/usr/share/zsh/site-functions*
 noextract=/usr/share/info*
 noextract=/usr/share/locale*
-noextract=/usr/lib/gconv*