Add comment to nrr_kind

According to Atmosphére (https://github.com/Atmosphere-NX/Atmosphere/blob/c7026b90940a1d88f9c10a6d98263bf22e654fa5/libraries/libstratosphere/include/stratosphere/ro/ro_types.hpp), nrr_kind (Atmosphére calls it "type") is 7.0.0+

src/core/hle/service/ldr/ldr.cpp

@@ -58,7 +58,7 @@ struct NRRHeader {
     std::array<u8, 0x100> signature;
     u64_le application_id;
     u32_le size;
-    u8 nrr_kind;
+    u8 nrr_kind; // 7.0.0+
     std::array<u8, 0x3> reserved_2;
     u32_le hash_offset;
     u32_le hash_count;