afdo_bisection: make docs slightly more helpful

BUG=None
TEST=None

Change-Id: I81c38a80d7b84ac4ae65a3e75b232a0131a3f5ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1846266
Reviewed-by: Caroline Tice <cmtice@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
diff --git a/afdo_tools/bisection/afdo_prof_analysis.py b/afdo_tools/bisection/afdo_prof_analysis.py
index 8455d2b..3653110 100755
--- a/afdo_tools/bisection/afdo_prof_analysis.py
+++ b/afdo_tools/bisection/afdo_prof_analysis.py
@@ -11,6 +11,13 @@
 file as arguments. Given these pieces of information, it analyzes the profiles
 to try and determine what exactly is bad about the bad profile. It does this
 with three main techniques: bisecting search, range search, and rough diff-ing.
+
+The external script communicates the 'goodness' of an AFDO profile through its
+exit code. The codes known to this script are:
+  - 0: the AFDO profile produced a good binary
+  - 1: the AFDO profile produced a bad binary
+  - 125: no result could be determined; just try another profile
+  - >127: quit immediately
 """
 
 from __future__ import division, print_function
@@ -395,6 +402,7 @@
 
 
 def main(flags):
+  logging.getLogger().setLevel(logging.INFO)
   if not flags.no_resume and flags.seed:  # conflicting seeds
     raise RuntimeError('Ambiguous seed value; do not resume from existing '
                        'state and also specify seed by command line flag')