Enhancement: Mnemonic image Input or output? for Guide, chapter 7 (Template Syntax)

[vpithart]

This is proposal to improve educational value of the Guide.

In the guide, chapter Template Syntax, there's paragraph Input or Output?.

When learning ng2, the following graphic mnemonic helped me to memorize which one of [] and () is Input or Output:

So I propose to enhance the input-output.png image this way.