cli: Add help text about argument exclusivity

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

Author: jku

README.md

@@ -87,10 +87,14 @@ optional arguments:
                        times to increase verbosity (default: 0)
   -V, --version        show program's version number and exit
   --staging            Use sigstore's staging instance, instead of the default
-                       production instance (default: False)
+                       production instance. Mutually exclusive with other
+                       instance configuration arguments. (default: False)
   --instance URL       Use a given Sigstore instance URL, instead of the
-                       default production instance (default: None)
-  --trust-config FILE  The client trust configuration to use (default: None)
+                       default production instance. Mutually exclusive with
+                       other instance configuration arguments. (default: None)
+  --trust-config FILE  The client trust configuration to use. Mutually
+                       exclusive with other instance configuration arguments.
+                       (default: None)
 ```
 <!-- @end-sigstore-help@ -->
 

sigstore/_cli.py

@@ -263,19 +263,28 @@ def _parser() -> argparse.ArgumentParser:
         "--staging",
         action="store_true",
         default=_boolify_env("SIGSTORE_STAGING"),
-        help="Use sigstore's staging instance, instead of the default production instance",
+        help=(
+            "Use sigstore's staging instance, instead of the default production instance."
+            " Mutually exclusive with other instance configuration arguments."
+        ),
     )
     global_instance_options.add_argument(
         "--instance",
         metavar="URL",
         type=str,
-        help="Use a given Sigstore instance URL, instead of the default production instance",
+        help=(
+            "Use a given Sigstore instance URL, instead of the default production instance."
+            " Mutually exclusive with other instance configuration arguments."
+        ),
     )
     global_instance_options.add_argument(
         "--trust-config",
         metavar="FILE",
         type=Path,
-        help="The client trust configuration to use",
+        help=(
+            "Use given client trust configuration, instead of using the default production"
+            " instance. Mutually exclusive with other instance configuration arguments."
+        ),
     )
     subcommands = parser.add_subparsers(
         required=True,