chore: suggest ext-sodium (#474)

Co-authored-by: Brent Shaffer <betterbrent@google.com>

Author: peter279k

composer.json

@@ -23,7 +23,8 @@
         "php": "^7.1||^8.0"
     },
     "suggest": {
-        "paragonie/sodium_compat": "Support EdDSA (Ed25519) signatures when libsodium is not present"
+        "paragonie/sodium_compat": "Support EdDSA (Ed25519) signatures when libsodium is not present",
+        "ext-sodium": "Support EdDSA (Ed25519) signatures"
     },
     "autoload": {
         "psr-4": {