add docs for HAProxy deployment

deploy/README.md

@@ -255,3 +255,17 @@ acme.sh --deploy -d fritzbox.example.com --deploy-hook fritzbox
 ```sh
 acme.sh --deploy -d ftp.example.com --deploy-hook strongswan
 ```
+
+## 10. Deploy the cert to HAProxy
+
+You must specify the path where you want the concatenated key and certificate chain written.
+```sh
+export DEPLOY_HAPROXY_PEM_PATH=/etc/haproxy
+```
+
+You can then deploy the certificate as follows
+```sh
+acme.sh --deploy -d haproxy.example.com --deploy-hook haproxy
+```
+
+The path for the PEM file will be stored with the domain configuration and will be available when renewing, so that deploy will happen automatically when renewed.