Update lab3.md assignment text

[milosonator]

Add an example on how layout in a syntax definition template is reflected in the pretty-printed output.

[guwac]

An illustrating example would indeed be useful here. @milosonator or @eduardosamorim, can you add a MiniJava example instead, e.g. a class declaration? Should consist of an example class, simple template rule which results in ugly pretty-printing, and adjusted template rule which results in pretty pretty-printing.

[milosonator]

I changed the example to a MiniJava example with normal template which results in poor pretty-printing and a template which makes the printed result more pretty.

[milosonator]

@guwac @udesou If possible, please check out my changes.