Add README section 'Finding your way in the codebase'

README.md

@@ -240,6 +240,36 @@ See the file `INSTALL.md` for a detailed usage and deployment guide. The file
 `ChangeLog` explains how to see the history log of the changes done in the
 code. `NEWS.md` provides a friendly overview of the changes for each release.
 
+## Finding your way in the codebase
+
+- `app`:
+  *main* functions of the web app, for regular build and for development modes
+- `config`:
+  Settings the app reads when it launches, some defined by a human and some
+  auto-generated
+- `_darcs`:
+  Internal version control data of this repo, similar to a `.git` directory
+- `embed`:
+  Files embedded into the app source code at build time (using TH)
+- `hook-darcs` & `hook-git`:
+  *main* functions for VCS hook programs to be inserted into every repo hosted
+  by the app
+- `migrations`:
+  Helper files for DB migrations: New entities added & model files for
+  migrations involving data manipulation
+- `src`:
+  Web app Haskell source code, built as a library whose modules are used by the
+  various executables
+- `static`:
+  Static files (such as CSS and fonts) served by the web app (no such files at
+  the moment)
+- `templates`:
+  UI page and widget templates (`.hamlet` for HTML, `.cassius` for CSS)
+- `test`:
+  No tests have been written yet
+- `th`:
+  Domain-specific language snippets, from which code is generated using TH
+
 ## Reporting Bugs and Suggesting Features
 
 If you found a bug, or you have an idea, a feature request or a wishlist item,