minor corrections

- Explained the sblock question
- There are no 'paths'. There is no 'flow'. There are only links!
- Moved the explanation of what the blocks do to a more logical place.
1) it is not stricly defined at all;
2) It is neither an official documentation, neither it has been approved by anyone. Even better, it is your own re-elaboration.
3) do no try to re-invent existing things.