Docs: Create issue template to cover common issues (#1808)

Author: callumacrae

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,28 @@
+This tracker is for bug reports only.
+
+
+Before opening an issue, please make sure you've checked the following:
+
+- For support requests, please use Stack Overflow (stackoverflow.com) or Gitter (see the README).
+
+- If the bug is in a plugin, open an issue on the plugin repository, not the gulp repository.
+
+- If you're getting a deprecated module warning, don't worry about it: we're aware of it and it's not an issue. To make it go away, update to Gulp 4.0.
+
+- If you're asking about the status of Gulp 4, please don't! You can see the remaining issues on the gulp4 label: https://github.com/gulpjs/gulp/issues?q=is%3Aissue+is%3Aopen+label%3Agulp4
+
+----
+
+**What were you expecting to happen?**
+
+**What actually happened?**
+
+**Please post a sample of your gulpfile (preferably reduced to just the bit that's not working)**
+
+```js
+gulp.task(function () {});
+```
+
+**What version of gulp are you using?**
+
+**What versions of npm and node are you using?**