Add a Github issue template.

That should give a helping hand to everyone.

Author: vphilippon

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,21 @@
+Be sure to check the existing issues, both open and closed.
+
+Describe the issue briefly here.
+
+##### Describe you environment
+
+1. OS Type
+1. Python version: `$ python -V`
+1. Pipenv version: `$ pipenv --version`
+
+##### Expected result
+
+Describe what you expected.
+
+##### Actual result
+
+When possible, provide the verbose output (`--verbose`), especially for locking and dependencies resolving issues.
+
+##### Steps to replicate
+
+Provide the steps to replicate (which usually at least includes the commands and the Pipfile).