add multi-subject example to docs

Signed-off-by: Brian DeHamer <[email protected]>

README.md

@@ -164,7 +164,7 @@ jobs:
           predicate: '{}'
 ```
 
-### Identify Subjects by Wildcard
+### Identify Multiple Subjects
 
 If you are generating multiple artifacts, you can generate an attestation for
 each by using a wildcard in the `subject-path` input.
@@ -180,6 +180,23 @@ each by using a wildcard in the `subject-path` input.
 For supported wildcards along with behavior and documentation, see
 [@actions/glob][8] which is used internally to search for files.
 
+Alternatively, you can explicitly list multiple subjects with either a comma or
+newline delimited list:
+
+```yaml
+- uses: actions/attest-build-provenance@v1
+  with:
+    subject-path: 'dist/foo, dist/bar'
+```
+
+```yaml
+- uses: actions/attest-build-provenance@v1
+  with:
+    subject-path: |
+      dist/foo
+      dist/bar
+```
+
 ### Container Image
 
 When working with container images you can invoke the action with the