[Minesweeper] draft approaches

[colinleach]

Just the introduction.md in this case. I couldn't identify such clearly different approaches that would justify separate sections.

I'll read this through again on Saturday, so there may be some minor corrections added.

[colinleach]

I made a few tweaks but couldn't think of anything major,

Over to you for comments. Meanwhile, I'll see how many more of these I can get drafted before this burst of enthusiasm drains away.