fix: don't ask for ed25519 gem if not using eddsa

Author: grzuy

README.md

@@ -57,6 +57,8 @@ algorithm.verify(signature, to_be_signed)
 Requires adding the `ed25519` gem to your `Gemfile`
 
 ```ruby
+require "openssl/signature_algorithm/eddsa"
+
 to_be_signed = "to-be-signed"
 
 # Signer

lib/openssl/signature_algorithm.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "openssl/signature_algorithm/ecdsa"
-require "openssl/signature_algorithm/eddsa"
 require "openssl/signature_algorithm/error"
 require "openssl/signature_algorithm/rsapss"
 require "openssl/signature_algorithm/rsapkcs1"