update markdown files

Change-Id: I26cb33017f4d808c87d2dab09078a5222db826f8
No-Try: true
Docs-Preview: https://skia.org/?cl=303956
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/303956
Commit-Queue: Zepeng Hu <[email protected]>
Reviewed-by: Kevin Lubick <[email protected]>

Author: Zepeng Hu

site/dev/testing/fuzz.md

@@ -31,3 +31,7 @@ To enumerate all supported types and names, run the following:
 
     out/ASAN/fuzz --help  # will list all types
     out/ASAN/fuzz -t api  # will list all names
+
+If the crash does not show up, try to add the flag --loops:
+
+    out/ASAN/fuzz -b /path/to/downloaded/testcase --loops <times-to-run>