Added a line to the README about argument precedence of long form and long form with value arguments

Author: moebrowne

README.md

@@ -128,6 +128,7 @@ The order the arguments are passed on the command line makes a difference
 
 * Calling `my-script.sh -f first -f last` will cause `argValue "f"` to return the value `last`
 * Calling `my-script.sh -g 345 -g` will mean cause `argValue "g"` to return nothing
+* Calling `my-script.sh --size 512 --size=1024` will mean cause `argValue "size"` to return 1024
 
 ## Debug Mode