Merge pull request #73 from joohoi/add-sewer

README: Add Sewer client

Author: joohoi

README.md

@@ -266,6 +266,7 @@ header_name = "X-Forwarded-For"
 ## Clients
 
 - acme.sh: [https://github.com/Neilpang/acme.sh](https://github.com/Neilpang/acme.sh)
+- Sewer: [https://github.com/komuw/sewer](https://github.com/komuw/sewer)
 
 ### Authentication hooks