release documentation - add antsibull-changelog command and fix fragm…

…ent location (#1413)

release documentation - add antsibull-changelog command and fix fragment location

SUMMARY
Running through community.aws 5.3.0 I noticed some minor mistakes
ISSUE TYPE

Docs Pull Request

COMPONENT NAME
docs/docsite/rst/collection_release.rst
ADDITIONAL INFORMATION

Reviewed-by: Alina Buzachis

docs/docsite/rst/collection_release.rst

@@ -239,7 +239,7 @@ While not strictly necessary it's preferable to add a release summary that will
 changelog.  For example, the `release summary for 5.2.0
 <https://ansible-collections.github.io/amazon.aws/branch/stable-5/collections/amazon/aws/docsite/CHANGELOG.html#release-summary>`_
 
-**changelog/fragments/release-summary.yml:**
+**changelogs/fragments/release-summary.yml:**
 
 .. code-block:: yaml
 
@@ -254,6 +254,10 @@ Generate the merged changelog
 Next we need to generate the merged changelog.  This will automatically delete the used fragments,
 update ``CHANGELOG.rst``, ``changelogs/changelog.yaml``, and ``git add`` what it changes.
 
+.. code-block:: bash
+
+  antsibull-changelog release
+
 Commit all of these changes to your local branch.
 
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