chore: update cran-comments to excuse the tarball size

Author: eitsupi

cran-comments.md

@@ -13,3 +13,8 @@
 ## R CMD check results
 
 - There were no ERRORs or WARNINGs.
+- Size of tarball is 9.5 MB (More than 5 MB).
+  - Most of this size is a tarball of vendored Rust source code,
+    since this package contains all the Rust source code of the dependencies.
+  - This package has always vendored Rust source code on CRAN since version 0.5.2
+    in September 2023, and the size has been over 9 MB.