doc: add documentation section in README file

README.md

@@ -109,3 +109,28 @@ Saves snapshots as golden values to a predefined source-controlled location (def
 
 Runs tests and verifies against previously-recorded golden values. Failures generate diffs at
 `/build/paparazzi/failures`.
+
+# Documentation
+
+The Mobile UI documentation is integrated in the [developer portal](https://developers.dhis2.org/). It 
+uses [Docusaurus](https://docusaurus.io), a modern tool to build documentation pages.
+
+The documentation is written in Markdown. The sidebar is automatically generated based on the metadata 
+of the different files. It follows the rules explained in the [autogenerated sidebar docs](https://docusaurus.io/docs/next/sidebar/autogenerated#autogenerated-sidebar-metadata). 
+In short, every file must have a `sidebar_position` label at the beginning of the document, which 
+defines the position of the document relative to its folder. Then, each folder has a `_category_.yml` 
+file, which has a `position` property defining the position of that folder relative to its parent folder.
+
+It is possible to nest as many folders as desired following that pattern.
+
+## Testing
+
+It is possible to build the Developers portal documentation to test your changes.
+
+Steps to test:
+1. Do the changes in the Mobile UI docs and push them to a branch in github.
+2. Download the [Deverlopers portal repository](https://github.com/dhis2/developer-portal).
+3. Change the branch in the Mobile UI block in the file `docs-migrate.js` to point to your branch.
+4. Follow the instructions in [CONTRIBUTING](https://github.com/dhis2/developer-portal/blob/main/CONTRIBUTING.md) 
+to build the docs.
+