Added Vagrant explanation

BUILD_GUIDE.md

@@ -1 +1,14 @@
-# Build Guide
+# Build Guide
+
+## Platform-specific setup
+
+### Windows
+
+
+### Mac
+
+
+### Linux
+
+### Vagrant
+If you have any problems building the firmware, you can try using a tool called Vagrant. It will set up a virtual computer with a known configuration that's ready-to-go for firmware building. OLKB does NOT host the files for this virtual computer. Details on how to set up Vagrant are in the [VAGRANT_GUIDE file](VAGRANT_GUIDE.md).