[libfuzzer] Clarify -max_len behavior on bigger files (llvm#123095)

Author: chfast

compiler-rt/lib/fuzzer/FuzzerFlags.def

@@ -14,8 +14,9 @@ FUZZER_FLAG_UNSIGNED(seed, 0, "Random seed. If 0, seed is generated.")
 FUZZER_FLAG_INT(runs, -1,
             "Number of individual test runs (-1 for infinite runs).")
 FUZZER_FLAG_INT(max_len, 0, "Maximum length of the test input. "
-    "If 0, libFuzzer tries to guess a good value based on the corpus "
-    "and reports it. ")
+  "Contents of corpus files are going to be truncated to this value. "
+  "If 0, libFuzzer tries to guess a good value based on the corpus "
+  "and reports it.")
 FUZZER_FLAG_INT(len_control, 100, "Try generating small inputs first, "
   "then try larger inputs over time.  Specifies the rate at which the length "
   "limit is increased (smaller == faster).  If 0, immediately try inputs with "