add use-cases to description templates (replaces !661)

doc/user/project/description_templates.md

@@ -22,6 +22,18 @@ Description templates must be written in [Markdown](../markdown.md) and stored
 in your project's repository under a directory named `.gitlab`. Only the
 templates of the default branch will be taken into account.
 
+## Use-cases
+
+- Add a template to be used in every issue for a specific project,
+giving instructions and guidelines, requiring for information specific to that subject.
+For example, if you have a project for tracking new blog posts, you can require the
+title, outlines, author name, author social media information, etc.
+- Following the previous example, you can make a template for every MR submitted
+with a new blog post, requiring information about the post date, frontmatter data,
+images guidelines, link to the related issue, reviewer name, etc.
+- You can also create issues and merge request templates for different
+stages of your workflow, e.g., feature proposal, feature improvement, bug report, etc.
+
 ## Creating issue templates
 
 Create a new Markdown (`.md`) file inside the `.gitlab/issue_templates/`