plugins/man: Add "R" to $LESS

Otherwise, `-R` must be added on the command line or colors just won't be rendered and these variables will be ignored.

plugins/available/man.plugin.bash

@@ -1,4 +1,4 @@
-cite about-plugin
+# shellcheck shell=bash
 about-plugin 'colorize man pages for better readability'
 
 export LESS_TERMCAP_mb=$'\e[1;32m'
@@ -8,3 +8,5 @@ export LESS_TERMCAP_se=$'\e[0m'
 export LESS_TERMCAP_so=$'\e[01;33m'
 export LESS_TERMCAP_ue=$'\e[0m'
 export LESS_TERMCAP_us=$'\e[1;4;31m'
+
+export LESS="R${LESS#-}"