Add Structure of other directories

Source-Code-Directory-Structure.md

@@ -22,3 +22,11 @@ You may need to become familiar with [Chromium's multi-process architecture](htt
 * **script** - Scripts for building atom-shell.
 
 ## Structure of other directories
+
+* **vendor** - Build dependencies.
+* **tools** - Helper scripts to build atom-shell.
+* **node_modules** - Third party node modules used for building or running specs.
+* **out** - Output directory for `ninja`.
+* **dist** - Temporary directory created by `script/create-dist.py` script when creating an distribution.
+* **node** - Downloaded node binary, it's built from https://github.com/atom/node/tree/chromium-v8.
+* **frameworks** - Downloaded third-party binaries of frameworks (only on Mac).