doc: add link to codebase overview in readme

README.md

@@ -74,6 +74,8 @@ Logseq is also made possible by the following projects:
 
 The following is for developers and designers who want to build and run Logseq locally and contribute to this project.
 
+We also have [a dedicated page](https://github.com/logseq/logseq/blob/master/CODEBASE_OVERVIEW.md) for LogSeq's codebase overview.
+
 ## Set up development environment
 
 ### 1. Requirements