Add an issue template to speed up issue resolution

ISSUE_TEMPLATE.md

@@ -0,0 +1,35 @@
+_[Description of the issue you are experiencing]_
+
+### Error Messages
+
+_List all the error messages or warnings you are seeing, if any._
+
+### Sample JSON
+
+```
+{
+ "key": "value"
+}
+```
+
+### Models
+
+_All models involved, including their `Decodable` implementations._
+
+```
+struct User {
+ // ...
+}
+
+extension User: Decodable {
+ // ...
+}
+```
+
+### Argo Version
+
+_example: Argo 3.0.0_
+
+### Dependency Manager
+
+_examples: Carthage, Cocoapods, git submodules, copied code, etc._