Merge bitcoin/bitcoin#28858: doc: rewrite explanation for -par=

d799ea2 doc: rewrite explanation for -par= (fanquake)

Pull request description:

  The negative bound for script threads comes from the machine which generates the man pages, so may only be correct for that machine. Any other placeholder value will also be wrong for some machines. Fix this be removing the value. This also fixes help2man incorrectly bolding the value, as if it were a paramater.

  Closes #28850.

ACKs for top commit:
  maflcko:
    lgtm ACK d799ea2
  theStack:
    ACK d799ea2

Tree-SHA512: 2eec0086faf4cc64bbf46b22949662f84d8546d2322c3d507fc44a4e1f64d228a2901af4fa4535c0771e3e14600be8308fc5dbd407b66ae6ae4f8878d8372c0a

src/init.cpp

@@ -455,8 +455,8 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-maxorphantx=<n>", strprintf("Keep at most <n> unconnectable transactions in memory (default: %u)", DEFAULT_MAX_ORPHAN_TRANSACTIONS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-mempoolexpiry=<n>", strprintf("Do not keep transactions in the mempool longer than <n> hours (default: %u)", DEFAULT_MEMPOOL_EXPIRY_HOURS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-minimumchainwork=<hex>", strprintf("Minimum work assumed to exist on a valid chain in hex (default: %s, testnet: %s, signet: %s)", defaultChainParams->GetConsensus().nMinimumChainWork.GetHex(), testnetChainParams->GetConsensus().nMinimumChainWork.GetHex(), signetChainParams->GetConsensus().nMinimumChainWork.GetHex()), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::OPTIONS);
-    argsman.AddArg("-par=<n>", strprintf("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)",
-        -GetNumCores(), MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-par=<n>", strprintf("Set the number of script verification threads (0 = auto, up to %d, <0 = leave that many cores free, default: %d)",
+        MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-persistmempool", strprintf("Whether to save the mempool on shutdown and load on restart (default: %u)", DEFAULT_PERSIST_MEMPOOL), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-persistmempoolv1",
                    strprintf("Whether a mempool.dat file created by -persistmempool or the savemempool RPC will be written in the legacy format "