Merge pull request #3347 from JamesTheAwesomeDude/master

Update README to reflect the fact that this is a general-purpose ACME client

README.md

@@ -89,6 +89,7 @@ https://github.com/acmesh-official/acmetest
 - [ZeroSSL.com CA](https://github.com/acmesh-official/acme.sh/wiki/ZeroSSL.com-CA)
 - [BuyPass.com CA](https://github.com/acmesh-official/acme.sh/wiki/BuyPass.com-CA)
 - [Pebble strict Mode](https://github.com/letsencrypt/pebble)
+- Any other [RFC8555](https://tools.ietf.org/html/rfc8555)-compliant CA
 
 # Supported modes