Document how to add external documentation for administrators of documentation

Author: stevepiercy

docs/contributing/admins.md

@@ -15,6 +15,42 @@ This guide is for administrators of Plone Documentation.
 It covers automated deployments, hosting, automated testing, previewing, and importing external package documentation into Plone Documentation.
 
 
+(administrators-import-docs-submodule-label)=
+
+## Importing external docs and converting to MyST
+
+This section describes how to import external projects and convert their docs to MyST.
+We did this for `plone.app.dexterity` and several other projects.
+
+1.  Create a new branch using the name of the project.
+1.  Install [rst-to-myst](https://pypi.org/project/rst-to-myst/).
+
+    ```shell
+    bin/pip install "rst-to-myst[sphinx]"
+    ```
+
+1.  Clone the project repository to the root of `plone/documentation`.
+1.  Delete any non-documentation files from the clone.
+1.  Move the documentation files and subfolders to the root of the clone, retaining the documentation structure.
+1.  Convert the reStructuredText documentation files to MyST.
+    The example commands below assume that there are files at the root of the clone and in one sub-level of nested directories. For deeper nesting, insert globbing syntax for each sub-level as `**/`
+
+    ```shell
+    bin/rst2myst convert -R project/*.rst
+    bin/rst2myst convert -R project/**/*.rst
+    ```
+
+1.  Add HTML meta data to the converted files.
+
+    ```shell
+    cd project
+    ../bin/python ../docs/addMetaData.py
+    ```
+
+1.  Optionally clean up any MyST syntax.
+1.  Commit and push your branch to GitHub and create a pull request.
+
+
 (administrators-import-docs-submodule-label)=
 
 ## Importing external docs with submodules