Merge bitcoin/bitcoin#32245: doc: Updates how to reproduce fuzz CI failure locally

8fe001d doc: Updates how to reproduce fuzz CI failure locally (Sergi Delgado Segura)

Pull request description:

  The current version of the doc does not explain how to reproduce a recent fuzzing CI failure (not yet part of the corpora). Add instructions on how to manually create a crash file based on a report.

ACKs for top commit:
  maflcko:
    lgtm ACK 8fe001d
  glozow:
    ACK 8fe001d

Tree-SHA512: 7436d71a30bbbffc34770027f1deeacca2de528d8d1b333431d6070c2ba779ecfcdaf25dc791d2154ba4dd37824d06aed2695a8412d7ca1f29e5bd1796d42aeb

Author: glozow

doc/fuzzing.md

@@ -136,6 +136,13 @@ Patience is useful; even with improved throughput, libFuzzer may need days and
 - run the fuzzer with the case number appended to the seed corpus path:
   `FUZZ=process_message build_fuzz/bin/fuzz
   qa-assets/fuzz_corpora/process_message/1bc91feec9fc00b107d97dc225a9f2cdaa078eb6`
+- If the file does not exist, make sure you are checking out the exact same commit id
+  for the qa-assets repo. If the file was found while running the fuzz engine in the CI,
+  you should be able to reproduce the crash locally  with the same (or a similar input)
+  within a few minutes. Alternatively, you can use the base64 encoded file from the CI log,
+  if it exists. e.g.
+  `echo "Nb6Fc/97AACAAAD/ewAAgAAAAIAAAACAAAAAoA==" |
+  base64 --decode > qa-assets/fuzz_corpora/process_message/1bc91feec9fc00b107d97dc225a9f2cdaa078eb6`
 
 ## Submit improved coverage