added pull request template

PULL_REQUEST_TEMPLATE.md

+**Please confirm you have done the following:**
+
+- [ ] I have read the [contributing guidelines](https://github.com/cam-rod/XKCDAltTextBot/wiki/Forking-and-Contributing-to-XKCDAltTextBot) and ensured that all error checking is properly working.
+
+**Add a summary of your modification and what it does:**
+
+
+
+**Add additional information (optional):*
+