Update tags release POST and PUT to be more specific.md

Originally submitted at
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5557.
Signed-off-by: Rémy Coutable <remy@rymai.me>

doc/api/tags.md

@@ -174,8 +174,19 @@ Parameters:
 
 - `id` (required) - The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user
 - `tag_name` (required) - The name of a tag
+
+Request body:
+
 - `description` (required) - Release notes with markdown support
 
+```json
+{
+  "description": "Amazing release. Wow"
+}
+```
+
+Response:
+
 ```json
 {
   "tag_name": "1.0.0",
@@ -195,8 +206,19 @@ Parameters:
 
 - `id` (required) - The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user
 - `tag_name` (required) - The name of a tag
+
+Request body:
+
 - `description` (required) - Release notes with markdown support
 
+```json
+{
+  "description": "Amazing release. Wow"
+}
+```
+
+Response:
+
 ```json
 {
   "tag_name": "1.0.0",