Improve the documentation for mooc-grader questionnaires

[saarasat]

More directives have been explained, some examples have been added and the content has been re-organized. This is not specifically related to any changes within the aplus, so this is mergeable even before any changes done aplus-questionnaires are put into production. The documentation works before and after those changes.

Testing

Changes have been manually tested after the changes done during the summer to the questionnaires as well as with the current production version.

Have you updated the README or other relevant documentation?

This would update and improve the documentation.

Is it Done?

Clean up your git commit history before submitting the pull request!

• [ ] I (developer) have created unit tests and the tests pass
• [ ] I (developer) have created functional tests (Selenium tests) if applicable
• [x] I (developer) have tested the changes manually
• [ ] Reviewer has finished the code review
• [ ] After the review, the developer has made changes accordingly
• [ ] Customer/Teacher has accepted the implementation of the feature

[markkuriekkinen]

@jaguarfi How do you feel about this PR since you have done other changes in the aplus-manual? I think these changes are useful. I could merge this PR if it is OK.

[markkuriekkinen]

The new instructions are much more better than before. However, I did some comments that may help to make the instructions even more readable. The question now is, who is going to continue working on this PR?

@jaguarfi You can continue with this and add new commits to the same branch.