Add note for CORINFO_FPSTRUCT_LOWERING::loweredElements type

src/coreclr/inc/corinfo.h

@@ -1909,6 +1909,8 @@ struct CORINFO_FPSTRUCT_LOWERING
     // Whether the struct should be passed by integer calling convention (cannot be passed by FP calling convention).
     bool byIntegerCallConv;
     // Types of lowered struct fields.
+    // Note: the integer field is denoted with a signed type reflecting size only so e.g. ushort is reported
+    // as CORINFO_TYPE_SHORT and Object or string is reported as CORINFO_TYPE_LONG.
     CorInfoType loweredElements[MAX_FPSTRUCT_LOWERED_ELEMENTS];
     // Offsets of lowered struct fields.
     uint32_t offsets[MAX_FPSTRUCT_LOWERED_ELEMENTS];