Document that hashes (`SHA1` header) aren't always SHA1

src/BizHawk.Client.Common/movie/HeaderKeys.cs

@@ -14,7 +14,7 @@ namespace BizHawk.Client.Common
 		public const string StartsFromSavestate = "StartsFromSavestate";
 		public const string StartsFromSaveram = "StartsFromSaveRam";
 		public const string SavestateBinaryBase64Blob = "SavestateBinaryBase64Blob"; // this string will not contain base64: ; it's implicit (this is to avoid another big string op to dice off the base64: substring)
-		public const string Sha1 = "SHA1";
+		public const string Sha1 = "SHA1"; // misleading name; either CRC32, MD5, or SHA1, hex-encoded, unprefixed
 		public const string FirmwareSha1 = "FirmwareSHA1";
 		public const string Pal = "PAL";
 		public const string BoardName = "BoardName";

src/BizHawk.Client.Common/movie/interfaces/IMovie.cs

@@ -90,7 +90,10 @@ namespace BizHawk.Client.Common
 		bool StartsFromSaveRam { get; set; }
 		string GameName { get; set; }
 		string SystemID { get; set; }
+
+		/// <value>either CRC32, MD5, or SHA1, hex-encoded, unprefixed</value>
 		string Hash { get; set; }
+
 		string Author { get; set; }
 		string Core { get; set; }
 		string EmulatorVersion { get; set; }

src/BizHawk.Emulation.Common/Database/GameInfo.cs

@@ -11,7 +11,10 @@ namespace BizHawk.Emulation.Common
 	{
 		string Name { get; }
 		string System { get; }
+
+		/// <value>either CRC32, MD5, or SHA1, hex-encoded, unprefixed</value>
 		string Hash { get; }
+
 		string Region { get; }
 		RomStatus Status { get; }
 		bool NotInDatabase { get; }