Added documentation for evidence collection, on release page

Added what release evidence is about.
Added summary json sample.

doc/user/project/releases/index.md

@@ -85,17 +85,82 @@ drag and drop files to it. Release notes are stored in GitLab's database.
 
 There are several ways to add release notes:
 
-- In the interface, when you create a new Git tag
-- In the interface, by adding a note to an existing Git tag
-- Using the GitLab API
-
-### New tag page with release notes text area
-
-![new_tag](img/new_tag.png)
-
-### Tags page with button to add or edit release notes for existing Git tag
-
-![tags](img/tags.png)
+- In the interface, when you create a new Git tag.
+- In the interface, by adding a note to an existing Git tag.
+- Using the GitLab API.
+
+To create a new tag, navigate to your project's **Repository > Tags** and
+click **New tag**. From there, you can fill the form with all the information
+about the release:
+
+![new_tag](img/new_tag_12_5.png "Creation of a new tag.")
+
+You can also edit an existing tag to add release notes:
+
+![tags](img/tags_12_5.png "Addition of note to an existing tag")
+
+## Release Evidence
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/26019) in GitLab 12.5.
+
+Each time a new release is created, specific related data is collected in
+parallel. This dataset will be a snapshot this new release (including linked
+milestones and issues) at moment of creation. Such collection of data will
+provide a chain of custody and facilitate processes like external audits, for example.
+
+The gathered Evidence data is stored in the database upon creation of a new
+release as a JSON object. In GitLab 12.5, a link to
+the Evidence data is provided for [each Release](#releases-list).
+
+Here's what this object can look like:
+
+```json
+{
+  "release": {
+    "id": 5,
+    "tag": "v4.0",
+    "name": "New release",
+    "project_id": 45,
+    "project_name": "Project name",
+    "released_at": "2019-06-28 13:23:40 UTC",
+    "milestones": [
+      {
+        "id": 11,
+        "title": "v4.0-rc1",
+        "state": "closed",
+        "due_date": "2019-05-12 12:00:00 UTC",
+        "created_at": "2019-04-17 15:45:12 UTC",
+        "issues": [
+          {
+            "id": 82,
+            "title": "The top-right popup is broken",
+            "author_name": "John Doe",
+            "author_email": "john@doe.com",
+            "state": "closed",
+            "due_date": "2019-05-10 12:00:00 UTC"
+          },
+          {
+            "id": 89,
+            "title": "The title of this page is misleading",
+            "author_name": "Jane Smith",
+            "author_email": "jane@smith.com",
+            "state": "closed",
+            "due_date": "nil"
+          }
+        ]
+      },
+      {
+        "id": 12,
+        "title": "v4.0-rc2",
+        "state": "closed",
+        "due_date": "2019-05-30 18:30:00 UTC",
+        "created_at": "2019-04-17 15:45:12 UTC",
+        "issues": []
+      }
+    ]
+  }
+}
+```
 
 <!-- ## Troubleshooting