Update INSTALL documentation

Added a section for enabling the nocsd theme.

INSTALL.md

@@ -28,6 +28,7 @@
     * [Whisker Menu](#whiker_menu)
     * [Sound theme](#startup_sound)
 * [HiDPI (experimental)](#hidpi)
+* [Disabling GNOME Client Side Decorations](#nocsd)
 * [Common issues](#common_issues)
 <!--te-->
 
@@ -638,6 +639,34 @@ The cursors in the theme do not support HiDPI but [Hackneyed](https://www.gnome-
 
 [[Return to Index]](#index)
 
+---
+<a name="nocsd"/>
+## Disabling GNOME Client Side Decorations
+
+To disable client side decorations for XFCE applications, you can install the the [libxfce4ui-nocsd](https://github.com/Xfce-Classic/libxfce4ui-nocsd) fork. *(Note: This library primarily affects XFCE applications.)*
+
+For XUbuntu users specifically, you can install libxfce4ui-nocsd from your package manager.
+
+  sudo apt install libxfce4ui-nocsd-2-0
+
+Then open the XFCE Settings Editor > xsettings > DialogsUseHeader (remove check). Alternatively, you can also perform this action from the following terminal command.
+
+  xfconf-query -c xsettings -p /Gtk/DialogsUseHeader -s false
+
+If you want to disable the CSD dialogue headers seen in most other GTK3 applications, you can also install the gtk3-nocsd package.
+
+  sudo apt install gtk3-nocsd.
+
+After installing, you may need to reboot your computer. The Chicago95 GTK theme includes an optional gtk3-nocsd theme to mask the headerbars into simple toolbar buttons. To enable the gtk3-nocsd theme, follow the bellow steps:
+
+- Navigate to the location you've installed Chicago95. From there, navigate further more to gtk-3.0 > gtk.css.
+- Scroll to the bottom of the gtk.css file. There are two comments stating, "Comment out for gtk3-nocsd theme" and two more comments stating, "Uncomment for gtk3-nocsd theme." Do so for the specified lines.
+- You can comment out a line C style seen in the below example.
+
+  /\* Commented gibberish \*/
+
+- Log out then log back in. You can see the affect if you open the application Software centre as an example.
+
 ---
 <a name="common_issues"/>