chore: sync base/README.md to current image contents

Author: rinsuki

base/README.md

@@ -20,7 +20,11 @@ Most other applications (and Go apps that require libc/cgo) should start with `g
 of the packages in `gcr.io/distroless/static`, and 
 
 * glibc
-* libssl
+* libssl and dependencies (zlib, libzstd)
+
+Note: Debian 13 base image does not include [OpenSSL legacy algorithms](https://docs.openssl.org/3.5/man7/OSSL_PROVIDER-legacy/#operations-and-algorithms).
+
+If you want to use them, you will need to add `openssl-legacy-provider` yourself.
 
 ## Usage