Improve installation documentation

[davelab6]

Users have trouble installing fontcrunch, as per http://typedrawers.com/discussion/997/installing-fontcrunch

[sladen]

In that case dying on -std=c++0x, although are those (experimental features) being used?

[behdad]

c++0x should be replaced with c++11 perhaps?

[khaledhosny]

The original failure is on std::hypot which seems to be a C++11 thing, so I think we should use -std=c++11, though I doubt this is going to fix the issue since he seems to be building on Mac OS X 10.6.

[behdad]

Or just reimplement hypot. Humm.. hypot is in math.h as well.

[khaledhosny]

It is failing on std::round as well, I guess we can use the C functions from math.h for both, but someone with access to such a machine needs to check if it fails on something else after that.