Merge pull request #8 from WebAssembly/tlively-patch-1

Fix castflags bit indices

Author: tlively

Diff for: proposals/custom-rtts/Overview.md

@@ -564,8 +564,8 @@ Note that the bits now have the following meanings:
 ```
 bit 0: source nullability
 bit 1: target nullability
-bit 3: source exactness
-bit 4: target exactness
+bit 2: source exactness
+bit 3: target exactness
 ```
 
 The other new instructions are encoded as follows: