diff --git a/BUILDING.md b/BUILDING.md
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@@ -1,4 +1,13 @@
 # Building
+## Git Submodules
+This project makes use of git submodules to import dependencies into the source tree.
+After cloning this repository using git, prior to building NSTool the dependencies need to be downloaded.
+Run these two commands to initialise and download the dependencies:
+```
+git submodule init
+git submodule update
+```
+
 ## Linux (incl. Windows Subsystem for Linux) & MacOS - Makefile
 ### Requirements
 * `make`