Suggested improvements for ”Adding Static Methods”

[koendehondt]

Besides the suggestions in this PR, I have some comments:

• In section 13.8, the method selector is missing from:

We also define a class method
IRSendStatic class >>

• At the end of section 13.13, https://github.com/evref-inria/pharo-vm/pull/2/files is coming out of nowhere. Probably it can be removed, but I did not do it because I do not know what the intention of the author was.
• In section 13.14, there is a paragraph starting with "Need more discussions". It is not clear whether or not this paragraph describes a TODO.
• In section 13.15 "Limits and conclusion", it reads "This tutorial misses:" and then a list. Is that an indication of a TODO, or is that the final text?