Readme improvements

[ChrisVilches]

• Quickstart: Create an example that does something more useful (easy to understand). And put a print capture.
• Refactor the "creation of nodes" and "custom nodes" sections. They are quite similar.
• Remove Node API section maybe?, it's more like a general explanation of nodes, not about creating nodes specifically.
• Add print capture in the top part (next to the logo)?
• It says Example #1: Creating a tree with many decorators but only has two.
• Section called ticking the tree has no text
• condition nodes actually don't return success when the condition evals to true. They tick the node and then copy the status.
• control nodes don't really resemble an if-else... they are more like a for cycle with a break. Quote: A control node decides the flow of the execution. In simpler words, it uses a certain logic to decide which branch to execute. This is where most of the similarities with a simple if-else come from.
• This is incorrect The code defined in on_tick is executed right after the child is ticked. Actually it's not on_tick but, it should be the code inside the block of tick_each_children.
• This is a bit strange: Or using inline logic in the DSL. Write something like You can also use the DSL for blah blah.
• Add "which is the self" → the self of the condition node.
• Grammar: and placing conditional nodes as a leaves