Document the new include-contributors option

This new config option will be available in GRM 0.19.0 (when PR GitTools#541  is merged).

docs/input/docs/configuration/default-configuration.md

@@ -20,6 +20,7 @@ create:
     sha-section-heading: "SHA256 Hashes of the release artifacts"
     sha-section-line-format: "- `{1}\t{0}`"
     allow-update-to-published: false
+    include-contributors: false
 export:
     include-created-date-in-title: false
     created-date-string-format: ''
@@ -135,7 +136,12 @@ control the look and feel of the generated release notes.
   - A boolean value which indicates whether or not updates can be applied to
         published releases. The default value is false. **NOTE:** This
         configuration option was added in version 0.11.0 of GitReleaseManager.
-
+- **include-contributors**
+  - A boolean value which indicates whether the list of contributors is included
+      in the release notes. A contributor is defined as soneone who opened an issue
+      or submitted a PR. **NOTE:** This configuration option was added in version
+      0.19.0 of GitReleaseManager .
+
 See the [example create configuration section](create-configuration) to see an
 example of how a footer can be configured.