Document faster throughput configuration

Author: agroce

doc/fuzzing.md

@@ -83,6 +83,10 @@ INFO: seed corpus: files: 991 min: 1b max: 1858b total: 288291b rss: 150Mb
 …
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+## Run without sanitizers for increased throughput
+
+Fuzzing on a harness compiled with `--with-sanitizers=address,fuzzer,undefined` is good for finding bugs. However, the very slow execution even under libFuzzer will limit the ability to find new coverage. A good approach is to perform occasional long runs without the additional bug-detectors (configure `--with-sanitizers=fuzzer`) and then merge new inputs into a corpus as described in the qa-assets repo (https://github.com/bitcoin-core/qa-assets/blob/main/.github/PULL_REQUEST_TEMPLATE.md).  Patience is useful; even with improved throughput, libFuzzer may need days and 10s of millions of executions to reach deep/hard targets.
+
 ## Reproduce a fuzzer crash reported by the CI
 
 - `cd` into the `qa-assets` directory and update it with `git pull qa-assets`