modify country discussion template

Add "data reading ongoing" status to country discussion template

.github/ISSUE_TEMPLATE/country-data-template-non-annexi.md

@@ -19,6 +19,7 @@ Status can be
 * **read**:  data has been read
 * **legacy**: data is available in the repository but not reproduceable
 * **no data**: there is no data in the submission
+* **reading**: data reading is ongoing
 
 Each entry has the following form