Content-wise the patch looks pretty good.  I agree with the recommendations.  A couple suggestions though: I would break up the 20 lines of command-line commands.  Right now that chunk is a bit too long to grasp meaningfully.  My suggestion would be to break it up into two sections with text in between: one for applying a patch to 2.x or 3.x, and the other for merging (forward-porting) from 3.x to 3.y, with a textual explanation of what the subsequent chunk of commands will do.

I would also state (or link to) something about forward-porting from 3.x to 3.y and that 2.7 should be kept separate (both of which I think the current patch assumes knowledge of).  I would also say (or link to) something about pushing all branches simultaneously.

Lastly, might it be worth explicitly dividing the Mercurial stuff into separate sections for (1) everyone, and (2) committers?  Putting the committer-specific stuff (e.g. instructions on merging and pushing changes) in a separate section will simplify things for the general contributor.