We used both "qemu" and "QEMU", let's use the lower-case version everywhere
since it's also the name of the binary and the version that people are
most familiar with.
The stuff under test/ is not only for the integeration tests, but also
for various other test-related stuff, so adjust the docs a bit.
I have no idea if this is going to cause rendering problems, and it is fairly
hard to check. So let's just merge this, and if it github markdown processor
doesn't like it, revert.
