add instructions to compile for python3
Using graph-tool-2.2.29.1 downloaded from http://graph-tool.skewed.de/download;
./configure
Will detect and use python2.x series only.
There are no instructions or "tip" to build graph-tool for python3. A normal user will have to wait about an hour just to find that an "import graph-tool" will fail on python3.
Maybe some warning in the "README" file for new users...