Re-add original installation instructions for FreeCAD <0.20

INSTALL.md

@@ -15,3 +15,19 @@ Refer to [the FreeCAD wiki](https://wiki.freecadweb.org/Preference_Packs#Distrib
 2. Activate the pack via Preferences -> General -> Preference packs -> Dracula -> Apply
 
 3. Boom! It's working
+
+#### FreeCAD <0.20
+
+If you are using a FreeCAD version before 0.20 you will need to do the following:
+
+1. Copy `dracula.qss` to `~/.FreeCAD/Gui/Stylesheets/` (Linux)
+   `/Users/[YOUR_USER_NAME]/Library/Preferences/FreeCAD/Gui/Stylesheets/`
+   (MacOS) or `C:/[INSTALLATION_PATH]/FreeCAD/data/Gui/Stylesheets/` (Windows)
+
+2. Rename `Dracula.cfg` to `user.cfg` and copy to `~/.FreeCAD/` (Linux)
+   `/Users/[YOUR_USER_NAME]/Library/Preferences/FreeCAD/` (MacOS) or
+   `C:/[INSTALLATION_PATH]/FreeCAD/data/` (Windows). Note that will override
+   any existing configuration - if you want to preserve your original
+   configuration, you will need to manually merge the two `user.cfg` files
+
+3. Boom! It's working