Add check for most to zshrc

`most` doesn't exist on every host I touch. This prevents having to
specify PAGER=less on hosts that don't have it.

.zshrc

@@ -13,10 +13,15 @@ fi
 
 source ~/.p10k/powerlevel10k.zsh-theme
 
+# These are pretty safe to assume exist
 export PATH=~/bin:$PATH
 export EDITOR=vim
 export VISUAL=$EDITOR
-export PAGER=most
+
+# most does not exist on every system I touch
+if [[ -a /usr/bin/most ]]; then
+    export PAGER=most
+fi
 
 HISTFILE=~/.zsh_history
 HISTSIZE=10000