Add issue_template (#6017)

.github/ISSUE_TEMPLATE.md

+Hi there,
+
+Thank you for opening an issue. Please note that we try to keep the Terraform
+issue tracker reserved for bug reports and feature requests. For general usage
+questions, please see: https://www.terraform.io/community.html.
+
+### Terraform Version
+Run `terraform -v` to show the version. If you are not running the latest
+version of Terraform, please upgrade because your issue may have already been
+fixed.
+
+### Affected Resource(s)
+Please list the resources as a list, for example:
+- aws_instance
+- dnsimple_record
+
+If this issue appears to affect multiple resources, it may be an issue with
+Terraform's core, so please mention this.
+
+### Terraform Configuration Files
+```hcl
+# Copy-paste your Terraform configurations here - for large Terraform configs,
+# please use a service like Dropbox and share a link to the ZIP file. For
+# security, you can also encrypt the files using our GPG public key.
+```
+
+### Debug Output
+Please provider a link to a GitHub Gist containing the complete debug output:
+https://www.terraform.io/docs/internals/debugging.html. Please do NOT paste the
+debug output in the issue; just paste a link to the Gist.
+
+### Panic Output
+If Terraform produced a panic, please provide a link to a GitHub Gist containing
+the output of the `crash.log`.
+
+### Expected Behavior
+What should have happened?
+
+### Actual Behavior
+What actually happened?
+
+### Steps to Reproduce
+Please list the steps requires to reproduce the issue, for example:
+1. `terraform apply`
+
+### Important Factoids
+Are there anything atypical about your accounts that we should know? For
+example: Running in EC2 Classic? Custom version of OpenStack? Tight ACLs?
+
+### References
+Are there any other GitHub issues (open or closed) or Pull Requests that should
+be linked here? For example:
+- GH-1234