Link to the upstream project has been added

README.md

@@ -182,10 +182,12 @@ dynTLS does not implement the ACME protocol itself. Instead, it delegates all AC
 In this repository, ACME-related scripts are placed under:
 
 - `contrib/acme/letsencrypt_master.sh`
-  Upstream ACME client script (reference), unchanged or only minimally modified.
+  Upstream ACME client script, unchanged.
 - `contrib/acme/letsencrypt_master_local.sh`
   Local variant with customized `dns-01` challenge handling, for example using Bind/nsupdate, TSIG and `rndc` to manage internal DNS zones.
 
+Both scripts are based on the upstream `ght-acme.sh` client (<https://github.com/bruncsak/ght-acme.sh>) and are licensed under the GNU GPLv2-or-later; see `LICENSE.md` and the script headers for details.
+  
 Example configuration in `vars`:
 
 ```bash
@@ -197,7 +199,7 @@ set_var DYNTLS_DNS_SERVER "root-dns.example365.tld"
 set_var DYNTLS_DNS_TSIG   "/opt/dyntls/private/tsig.key"
 ```
 
-You can replace this with other ACME clients (e.g. acme.sh, lego) by pointing DYNTLS_LE_PROGRAM to your preferred script and ensuring its CLI options match your setup.
+You can replace this with other ACME clients (e.g. acme.sh, lego) by pointing `DYNTLS_LE_PROGRAM` to your preferred script and ensuring its CLI options match your setup.
 
 ## License