message: Added ISPC_FP64_SUPPORTED to documentation
diff: @@ -803,6 +803,9 @@ preprocessor runs:
  * - ISPC_UINT_IS_DEFINED
  - 1.
  - Detecting if uint8/uint16/uint32/uint64 types are defined in the ISPC version.
  + * - ISPC_FP64_SUPPORTED
  + - 1.
  + - Detecting if double type is supported by the target.
  ``ispc`` supports the following ``#pragma`` directives.
  