Update issue templates

Author: soxoj

.github/ISSUE_TEMPLATE/add-a-site.md

@@ -0,0 +1,13 @@
+---
+name: Add a site
+about: I want to add a new site for Maigret checks
+title: New site
+labels: new-site
+assignees: soxoj
+
+---
+
+Link to the site main page: https://example.com
+Link to an existing account: https://example.com/users/john
+Link to a nonexistent account: https://example.com/users/noonewouldeverusethis7
+Tags: photo, us, ...