Add information about Composer packages

doc/user/packages/workflows/project_registry.md

@@ -77,6 +77,11 @@ depending on your final package recipe. For example:
 CONAN_LOGIN_USERNAME=<gitlab-username> CONAN_PASSWORD=<personal_access_token> conan upload MyPackage/1.0.0@foo+bar+my-proj/channel --all --remote=gitlab
 ```
 
+### Composer
+
+You can't publish a Composer package outside of its project. An [issue](https://gitlab.com/gitlab-org/gitlab/-/issues/250633)
+exists to implement functionality that allows you to publish such packages to other projects.
+
 ### All other package types
 
 [All package types supported by GitLab](../index.md) can be published in