Add link to previous commit (BACKSLASH_X_AS_BYTES)

std/json/decode_quirks.wuffs

diff --git a/std/json/decode_quirks.wuffs b/std/json/decode_quirks.wuffs
index c74c7b5..7802640 100644
--- a/std/json/decode_quirks.wuffs
+++ b/std/json/decode_quirks.wuffs
@@ -78,8 +78,9 @@
 // (0x4909_9400 | 0x08) is reserved for QUIRK_ALLOW_BACKSLASH_X_AS_BYTES. This
 // quirk used to be implemented, but it was removed due to its complexity.
 // Enabling it (as a run-time option) meant that decoded JSON strings are no
-// longer guaranteed to be valid UTF-8. We could re-implement it if there is
-// sufficient demand.
+// longer guaranteed to be valid UTF-8. We could re-implement it (i.e. undo
+// commit 6c138776) if there is sufficient demand.
+// https://github.com/google/wuffs/commit/6c138776889418bb155b748630e73f386b57a381
 
 // When this quirk is enabled, e.g. "abc\xeFz" is accepted as a JSON string. It
 // decodes to 6 bytes: 0x61, 0x62, 0x63, 0xC3, 0xAF and 0x7A. The UTF-8