Update of issue template

Added warning messages before reporting an issue

.github/ISSUE_TEMPLATE/problem.md

@@ -4,21 +4,23 @@ about: Open an issue to report a problem with the INSPIRE validator or test resu
 
 ---
 
-Before reporting an issue with the INSPIRE validator deployed at JRC, please check the [list of known limitations](https://github.com/INSPIRE-MIF/helpdesk-validator/wiki/Known-limitations).
+Before reporting an issue with the INSPIRE Reference Validator deployed at JRC, please:
+- check whether a similar issue has already been opened
+- try to validate your resource after cleaning the browser cache (in case of error during the upload of the resource) 
+- check the [list of known limitations](https://github.com/INSPIRE-MIF/helpdesk-validator/wiki/Known-limitations).
 
-Please replace these lines with a brief summary of your issue and the expected
-behaviour.
+To report an issue, please replace these lines with a brief summary of your issue and the expected behaviour.
 
 To help us investigate the issue, you may want to include:
 
-- [ ] a description of the steps to reproduce your issue
-- [ ] the browser and version used
-- [ ] a screenshot illustrating the problem
-- [ ] the Test Report (ideally as an attachment to the issue)
-- [ ] the name of the Test that failed or better: change the `Level of Detail`
+- a description of the steps to reproduce your issue
+- the browser and version used
+- a screenshot illustrating the problem
+- the Test Report (ideally as an attachment to the issue)
+- the name of the Test that failed or better: change the `Level of Detail`
 in the Report by clicking on `All Details`, then scroll down to the failed test
 and copy the Link on the right-hand side of the `Assertion URI`
-- [ ] the URL of your service / the file you have uploaded or referenced (as
+- the URL of your service / the file you have uploaded or referenced (as
 an attachment).
 
 If your service is protected or you have confidential data that you cannot