Clarify random theme setting (#7090)

Clarify random theme setting, in particular how to know
which theme was loaded if picked at random.

templates/zshrc.zsh-template

@@ -4,23 +4,23 @@
 # Path to your oh-my-zsh installation.
 export ZSH=$HOME/.oh-my-zsh
 
-# Set name of the theme to load. Optionally, if you set this to "random"
-# it'll load a random theme each time that oh-my-zsh is loaded.
+# Set name of the theme to load --- if set to "random", it will
+# load a random theme each time oh-my-zsh is loaded, in which case,
+# to know which specific one was loaded, run: echo $RANDOM_THEME
 # See https://github.com/robbyrussell/oh-my-zsh/wiki/Themes
 ZSH_THEME="robbyrussell"
 
-# Set list of themes to load
-# Setting this variable when ZSH_THEME=random
-# cause zsh load theme from this variable instead of
-# looking in ~/.oh-my-zsh/themes/
-# An empty array have no effect
+# Set list of themes to pick from when loading at random
+# Setting this variable when ZSH_THEME=random will cause zsh to load
+# a theme from this variable instead of looking in ~/.oh-my-zsh/themes/
+# If set to an empty array, this variable will have no effect.
 # ZSH_THEME_RANDOM_CANDIDATES=( "robbyrussell" "agnoster" )
 
 # Uncomment the following line to use case-sensitive completion.
 # CASE_SENSITIVE="true"
 
-# Uncomment the following line to use hyphen-insensitive completion. Case
-# sensitive completion must be off. _ and - will be interchangeable.
+# Uncomment the following line to use hyphen-insensitive completion.
+# Case-sensitive completion must be off. _ and - will be interchangeable.
 # HYPHEN_INSENSITIVE="true"
 
 # Uncomment the following line to disable bi-weekly auto-update checks.
@@ -57,7 +57,8 @@ ZSH_THEME="robbyrussell"
 # Would you like to use another custom folder than $ZSH/custom?
 # ZSH_CUSTOM=/path/to/new-custom-folder
 
-# Which plugins would you like to load? (plugins can be found in ~/.oh-my-zsh/plugins/*)
+# Which plugins would you like to load?
+# Standard plugins can be found in ~/.oh-my-zsh/plugins/*
 # Custom plugins may be added to ~/.oh-my-zsh/custom/plugins/
 # Example format: plugins=(rails git textmate ruby lighthouse)
 # Add wisely, as too many plugins slow down shell startup.