HACKING: Make mention of the separate cairo-traces repo

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>
perf: Move macro-benchmark documentation to cairo-traces

The macro benchmarks were moved to a separate repository some time ago,
but the perf README still refers to these tests as if they were still
present, which may lead to some confusion.  Instead, consolodate the
macro benchmark documentation with the macro benchmarks, and focus this
README on just the (still in tree) micro-benchmarks.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>