update cran comments

Author: h-a-graham

cran-comments.md

@@ -1,6 +1,6 @@
 ## R CMD check results
 
-Duration: 1m 8.1s
+Duration: 1m 52.9s
 
 ❯ checking for future file timestamps ... NOTE
   unable to verify current time
@@ -11,4 +11,9 @@ Duration: 1m 8.1s
 
 0 errors ✔ | 0 warnings ✔ | 2 notes ✖
 
-* This is a new release.
+* This is a follow-up to the initial CRAN release (0.2.0). The main change
+  is a new internal representation for `a5_cell` that stores cell IDs as
+  eight raw-byte fields instead of hex strings, reducing memory by ~10x and
+  eliminating hex parsing overhead at the R/Rust boundary. This redesign
+  was developed in collaboration with Felix Palmer, maintainer of the
+  upstream A5 Rust crate.