Add docs about key-value-delimiter

flags.go

@@ -66,6 +66,15 @@ line, you specify the value for such an option as key:value. For example
 Then, the AuthorInfo map can be filled with something like
 -a name:Jesse -a "surname:van den Kieboom".
 
+You can also specify key-value-delimiter.
+
+	type Options struct {
+	    AuthorInfo string[string] `short:"a" key-value-delimiter:"="`
+	}
+
+In this case, the AuthorInfo map can be filled with something like
+-a name=Jesse -a "surname=van den Kieboom".
+
 Finally, for full control over the conversion between command line argument
 values and options, user defined types can choose to implement the Marshaler
 and Unmarshaler interfaces.
@@ -111,6 +120,10 @@ The following is a list of tags for struct fields supported by go-flags:
 	                e.g. `long:"animal" choice:"cat" choice:"dog"`
 	hidden:         if non-empty, the option is not visible in the help or man page.
 
+	key-value-delimiter:  when specified on a map field, the key and the value are
+	                      separated with the given delimiter string,
+	                      instead of the default delimiter ":" (optional)
+
 	base: a base (radix) used to convert strings to integer values, the
 	      default base is 10 (i.e. decimal) (optional)