docs(custom): update comments in example files (#11727)

custom/example.zsh

-# You can put files here to add functionality separated per file, which
-# will be ignored by git.
-# Files on the custom/ directory will be automatically loaded by the init
-# script, in alphabetical order.
-
-# For example: add yourself some shortcuts to projects you often work on.
+# Put files in this folder to add your own custom functionality.
+# See: https://github.com/ohmyzsh/ohmyzsh/wiki/Customization
+# 
+# Files in the custom/ directory will be:
+# - loaded automatically by the init script, in alphabetical order
+# - loaded last, after all built-ins in the lib/ directory, to override them
+# - ignored by git by default
+# 
+# Example: add custom/shortcuts.zsh for shortcuts to your local projects
 # 
 # brainstormr=~/Projects/development/planetargon/brainstormr
 # cd $brainstormr
-#

custom/plugins/example/example.plugin.zsh

 # Add your own custom plugins in the custom/plugins directory. Plugins placed
 # here will override ones with the same name in the main plugins directory.
+# See: https://github.com/ohmyzsh/ohmyzsh/wiki/Customization#overriding-and-adding-plugins

custom/themes/example.zsh-theme

 # Put your custom themes in this folder.
+# See: https://github.com/ohmyzsh/ohmyzsh/wiki/Customization#overriding-and-adding-themes
+# 
 # Example:
 
 PROMPT="%{$fg[red]%}%n%{$reset_color%}@%{$fg[blue]%}%m %{$fg[yellow]%}%~ %{$reset_color%}%% "