Tweak FUZZING.md and minimise_corpuses.sh.

Change-Id: If312ce3783bcc39ebd2047470251334aa0897d3d
Reviewed-on: https://boringssl-review.googlesource.com/7508
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/fuzz/minimise_corpuses.sh b/fuzz/minimise_corpuses.sh
index 4b279de..5f9ade5 100644
--- a/fuzz/minimise_corpuses.sh
+++ b/fuzz/minimise_corpuses.sh
@@ -25,7 +25,6 @@
   test=$(echo $testSource | sed -e 's/\.cc$//')
   mv ${test}_corpus ${test}_corpus_old
   mkdir ${test}_corpus
-  $buildDir/fuzz/$test -max_len=50000 -runs=0 -save_minimized_corpus=1 \
-    ${test}_corpus ${test}_corpus_old
+  $buildDir/fuzz/$test -max_len=50000 -merge=1 ${test}_corpus ${test}_corpus_old
   rm -Rf ${test}_corpus_old
 done