update README

Author: ko1

README.md

@@ -667,6 +667,7 @@ The `<...>` notation means the argument.
   * `info ivars <expr>` shows the instance variables of the result of `<expr>`.
 * `i[nfo] c or consts or constants`
   * Show information about accessible constants except toplevel constants.
+  * `info consts <expr>` shows the constants of a class/module of the result of `<expr>`
 * `i[nfo] g or globals or global_variables`
   * Show information about global variables
 * `i[nfo] th or threads`