Add quickstart.txt

There's not much documentation for meliae in the source tree. You have to search the net for some blog posts, but those are a bit tl;dr for someone just wanting to see if the tool even works at all, or otherwise doesn't need very careful analysis (yet).

e.g. I just saw someone in #twisted get completely stuck trying to figure out how to use it. They found red herrings (track_memory.py) and blog posts that explained step-by-step how to look at dumps, and they had no clue how to make a dump in the first place.

Basically I think what's needed is some instructions in the README or in a QuickStart.txt along the lines of:

 1. In your program you want to analyse, run meliae.scanner.dump_<something>
 2. Start a new Python interpreter
 3. load that dump
 4. examine it interactively.
 5. (if you want to know more, see X, Y, and Z)