Update issue templates

add user case issues template

.github/ISSUE_TEMPLATE/user-case.md

@@ -0,0 +1,20 @@
+---
+name: user case
+about: Describe this issue template's purpose here.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+### Application name 
+XXX   
+### Target users 
+Describe why your application was created for what users. 
+### What can it be used for? 
+Briefly describe the purpose of your application creation and what problems it solves for people 
+### Application address 
+If you want to share your app so more people can see it, you can leave the link to use your app here. 
+### How was it made?  
+You can share how you created this amazing app step by step based on Dify. 
+### Product Screenshots (optional)