On a bootc host print the BOOTC_HOST_DOC if available.

dnf/cli/cli.py

@@ -215,7 +215,13 @@ def do_transaction(self, display=()):
                 logger.info(_("{prog} will only download packages, install gpg keys, and check the "
                               "transaction.").format(prog=dnf.util.MAIN_PROG_UPPER))
             if dnf.util._is_bootc_host():
-                _bootc_host_msg = _("""
+                bootc_docs = dnf.util._bootc_doc_url()
+                if bootc_docs:
+                    _bootc_host_msg = _("""
+*** Error: system is configured to be read-only; for more
+*** information see: """ + dnf.util._bootc_doc_url())
+                else:
+                    _bootc_host_msg = _("""
 *** Error: system is configured to be read-only; for more
 *** information run `bootc status` or `ostree admin status`.
 """)

dnf/util.py

@@ -656,3 +656,12 @@ def _is_bootc_host():
     # temporary changes (until reboot).
     return os.path.isfile(ostree_booted) and not os.access(usr, os.W_OK)
 
+
+def _bootc_doc_url():
+    try:
+        with open('/etc/os-release', 'r') as f:
+            for line in f:
+                if line.startswith('BOOTC_HOST_DOC='):
+                    return line.split('=')[1].strip().strip('"')
+    except Exception as e:
+        return None