(docs) change and expact Arity section in getting started guide

Author: jcubic

docs/docs/intro.mdx

@@ -134,10 +134,11 @@ If you type `hello Terminal` it will print "hello, this is Terminal"
 
 ## Terminal Options
 
-### Arity
+### Variable number of arguments
 
-If you want the argument to be optional you need to `checkArity: false` option (options is
-an object that is a second argumnet to the termianal).
+If you want the argument to be optional you need to `checkArity: false` option (options is an object
+that is a second argumnet to the termianal). Variable number of arguments is so called
+[Arity](https://en.wikipedia.org/wiki/Arity).
 
 ```javascript
 $('body').terminal({