fuzz: Update README

Author: nwellnhof

fuzz/README.md

@@ -12,6 +12,12 @@ meaningful stack traces.
         -fno-sanitize-recover=all \
         -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION"
 
+Since llvm-symbolizer can use libxml2 itself, you may need the following
+wrapper to make sure that it doesn't use the instrumented version of
+libxml2:
+
+    export ASAN_SYMBOLIZER_PATH="$(pwd)/.gitlab-ci/llvm-symbolizer"
+
 Other options that can improve stack traces:
 
     -fno-omit-frame-pointer