docs: add clarifying note in the README about null values (#300)

* readme: Add clarifying note about null values

* readme: Remove duplicate documentation of null values

README.md

@@ -85,8 +85,15 @@ This is a diagram of how the theme is split between its components.
 ## Configuration options
 
 All flavors support certain levels of customization that match our [Catppuccin
-Style Guide][style-guide]. To add these customizations, add any of the following
-options to your Tmux configuration.
+Style Guide][style-guide]. To add these customizations, you may add any of the
+following options to your Tmux configuration.
+
+If you want to set a text-based customization to an emtpy string, use `null` to
+do so. For instance:
+
+```sh
+set -g @catppuccin_icon_window_last "null"
+```
 
 ### Window
 
@@ -340,16 +347,6 @@ set -g @catppuccin_[module_name]_color "color"
 set -g @catppuccin_[module_name]_text "text"
 ```
 
-#### Removing a specific module option
-```sh
-set -g @catppuccin_[module_name]_[option] "null"
-```
-This is for the situation where you want to remove the icon from a module.
-Ex:
-```sh
-set -g @catppuccin_date_time_icon "null"
-```
-
 ### Battery module
 
 #### Requirements