Add basic issue template; first crack at resolving #76

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,13 @@
+If the issue you're having is related to color rendering or incorrect colors, **please ensure that you have carefully read and gone through the Installation section of the README at https://github.com/joshdick/onedark.vim#installation before submitting your issue.**
+
+(If not a feature request)
+
+Output from `vim --version`:
+
+```
+Replace this text with the output
+```
+
+Terminal emulator(s) and their version(s) used, if applicable: `Replace this text if applicable, or delete this line`
+
+Thank you!