Provide more context for performance figures.

README

@@ -34,6 +34,9 @@ Some parsing performance figures:
 
 On a 2.3Ghz Corei5, apachedex achieves 97000 lines/s (
 pypy-c-jit-62994-bd32583a3f11-linux64) and 43000 lines/s (CPython 2.7).
+Those were measures on a 3000000-hits logfile, with 3 --skip-base, 1
+--erp5-base, 3 --base and --default set. --*base values were similar in
+simplicity to the ones provided in examples below.
 
 What APacheDEX is not
 =====================