add warning and version number at top of auto-generated Native.Raw.cs

Author: warrenfalk

RocksDbSharp/Native.Raw.cs

@@ -1,3 +1,6 @@
+/* WARNING: This file was autogenerated from version v5.18.3 of rocksdb/c.h at
+   https://raw.githubusercontent.com/facebook/rocksdb/v5.18.3/include/rocksdb/c.h
+ */
 using System;
 using System.Runtime.InteropServices;
 using byte_ptr = System.IntPtr;
@@ -4011,4 +4014,4 @@ public abstract uint64_t rocksdb_approximate_memory_usage_get_cache_total(
 
     } // class Native
     #endregion // Transaction Options
-} // namespace RocksDbSharp
+} // namespace RocksDbSharp