Improve comment explaining purpose of MAX_MONEY constant

src/amount.h

@@ -16,7 +16,15 @@ typedef int64_t CAmount;
 static const CAmount COIN = 100000000;
 static const CAmount CENT = 1000000;
 
-/** No amount larger than this (in satoshi) is valid */
+/** No amount larger than this (in satoshi) is valid.
+ *
+ * Note that this constant is *not* the total money supply, which in Bitcoin
+ * currently happens to be less than 21,000,000 BTC for various reasons, but
+ * rather a sanity check. As this sanity check is used by consensus-critical
+ * validation code, the exact value of the MAX_MONEY constant is consensus
+ * critical; in unusual circumstances like a(nother) overflow bug that allowed
+ * for the creation of coins out of thin air modification could lead to a fork.
+ * */
 static const CAmount MAX_MONEY = 21000000 * COIN;
 inline bool MoneyRange(const CAmount& nValue) { return (nValue >= 0 && nValue <= MAX_MONEY); }