Split the issue template into multiple files

ISSUE_TEMPLATE/integration.md

@@ -0,0 +1,20 @@
+---
+name: Suggest a new linter or fixer
+about: Suggest a new tool ALE can officially integrate with
+
+---
+
+<!--
+  Write "Add support for foobar" as the issue title, or similar.
+
+  Fill out the details below.
+-->
+
+**Name:** foobar
+**URL:** https://foo.bar.com
+
+<!--
+  Write a description of the tool, and add any other information you think might
+  be helpful. Consider creating a pull request to add support for the tool
+  yourself.
+-->