instructions about how to paste YAML or JSON code

Hopefully that will make issues easier to read.

.github/ISSUE_TEMPLATE.md

@@ -13,7 +13,19 @@ Also please indicate in the issue title which language/library is concerned. Eg:
 
 ##### Swagger declaration file content or url
 
-<!-- if it is a bug, a json or yaml that produces it. -->
+<!-- if it is a bug, a json or yaml that produces it.
+    If you post the code inline, please wrap it with
+    ```yaml
+    (here your code)
+    ```
+    (for YAML code) or
+    ```json
+    (here your code)
+    ```
+    (for JSON code), so it becomes more readable. If it is longer than about ten lines,
+    please create a Gist (https://gist.github.com) or upload it somewhere else and
+    link it here.
+  -->
 
 ##### Command line used for generation