docs: document DocSearch functionality (#419)

Co-authored-by: David Sanders <dsanders11@ucsbalum.com>

README.md

@@ -49,7 +49,15 @@ yarn pre-build ../relative/path/to/local/electron/repo
 yarn start
 ```
 
-# Repository content organization
+## Search indexing
+
+The search functionality on electronjs.org is powered by [Algolia DocSearch](https://docsearch.algolia.com/). DocSearch is a program run by Algolia that offers free
+documentation search for open source projects.
+
+If you are a maintainer with an @electronjs.org email, please message [@erickzhao](https://github.com/erickzhao)
+to be added to the Algolia project.
+
+## Repository content organization
 
 This repository contains the code for two related things: