Add monorepo workflows to package registry docs

doc/user/packages/package_registry/index.md

@@ -118,6 +118,9 @@ The **Packages & Registries > Package Registry** entry is removed from the sideb
 
 ## Package workflows
 
-Learn how to use the GitLab Package Registry to build your own custom package workflow.
+Learn how to use the GitLab Package Registry to build your own custom package workflow:
 
-- [Use a project as a package registry](../workflows/project_registry.md) to publish all of your packages to one project.
+- [Use a project as a package registry](../workflows/project_registry.md)
+  to publish all of your packages to one project.
+
+- Publish multiple different packages from one [monorepo project](../workflows/working_with_monorepos.md).

doc/user/packages/workflows/working_with_monorepos.md

+---
+stage: Package
+group: Package
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# Monorepo package management workflows
+
+One project or Git repository can contain multiple different subprojects or submodules that are all
+packaged and published individually.
+
+## Publishing different packages to the parent project
+
+The number and name of packages you can publish to one project is not limited.
+You can accomplish this by setting up different configuration files for each
+package. See the documentation for the package manager of your choice since
+each has its own specific files and instructions to follow to publish
+a given package.
+
+The example here uses [NPM](../npm_registry/index.md).
+In this example, `MyProject` is the parent project. It contains a sub-project `Foo` in the
+`components` directory:
+
+```plaintext
+MyProject/
+  |- src/
+  |   |- components/
+  |       |- Foo/
+  |- package.json
+```
+
+The goal is to publish the packages for `MyProject` and `Foo`. Following the instructions in the
+[GitLab NPM registry documentation](../npm_registry/index.md),
+you can publish `MyProject` by modifying the `package.json` file with a `publishConfig` section,
+and by doing one of the following:
+
+- Modify your local NPM configuration with CLI commands like `npm config set`.
+- Save a `.npmrc` file in the root of the project specifying these configuration settings.
+
+If you follow the instructions, you can publish `MyProject` by running `npm publish` from the root
+directory.
+
+Publishing `Foo` is almost exactly the same. Simply follow the same steps while in the `Foo`
+directory. `Foo` needs its own `package.json` file, which you can add manually by using `npm init`.
+`Foo` also needs its own configuration settings. Since you are publishing to the same place, if you
+used `npm config set` to set the registry for the parent project, then no additional setup is
+necessary. If you used an `.npmrc` file, you need an additional `.npmrc` file in the `Foo` directory.
+Be sure to add `.npmrc` files to the `.gitignore` file or use environment variables in place of your
+access tokens to prevent your tokens from being exposed. This `.npmrc` file can be identical to the
+one you used in `MyProject`. You can now run `npm publish` from the `Foo` directory and you can
+publish `Foo` separately from `MyProject`.
+
+You could follow a similar process for Conan packages. However, instead of `.npmrc` and
+`package.json`, you have `conanfile.py` in multiple locations within the project.
+
+## Publishing to other projects
+
+A package is associated with a project on GitLab, but the package does not need to be associated
+with the code in that project. When configuring NPM or Maven, you only use the `Project ID` to set
+the registry URL that the package uploads to. If you set this to any project that you have access to
+and update any other configuration similarly depending on the package type, your packages are
+published to that project. This means you can publish multiple packages to one project, even if
+their code does not exist in the same place. See the [project registry workflow documentation](project_registry.md)
+for more information.