Add section to docs about multiple registries

doc/user/packages/npm_registry/index.md

@@ -286,6 +286,22 @@ By default, when an NPM package is not found in the GitLab NPM Registry, the req
 
 Administrators can disable this behavior in the [Continuous Integration settings](../../admin_area/settings/continuous_integration.md).
 
+### Installing packages from other organizations
+
+You can route package requests to organizations and users outside of GitLab.
+
+To do this, add lines to your `.npmrc` file, replacing `my-org` with the namespace or group that owns your project's repository. The name is case-sensitive and must match the name of your group or namespace exactly. 
+
+```shell
+@foo:registry=https://gitlab.example.com/api/v4/packages/npm/
+//gitlab.com/api/v4/packages/npm/:_authToken=
+//gitlab.com/api/v4/projects/<your_project_id>/packages/npm/:_authToken= "<your_token>"
+
+@my-other-org:registry=https://gitlab.example.com/api/v4/packages/npm/
+//gitlab.com/api/v4/packages/npm/:_authToken=
+//gitlab.com/api/v4/projects/<your_project_id>/packages/npm/:_authToken= "<your_token>"
+```
+
 ## Removing a package
 
 In the packages view of your project page, you can delete packages by clicking