Add link to the guidelines for this repository

.github/ISSUE_TEMPLATE.md

@@ -1,4 +1,4 @@
-Thanks for wanting to report an issue you've found. 
+Before you submit an issue, please review **[the guidelines for this repository](https://github.com/tesseract-ocr/tesseract/blob/master/CONTRIBUTING.md)**.
 
 For support, first read the [Wiki](https://github.com/tesseract-ocr/tesseract/wiki), particularly the [FAQ](https://github.com/tesseract-ocr/tesseract/wiki/FAQ) to see if your problem is addressed there. If not, search the [Tesseract user forum](https://groups.google.com/d/forum/tesseract-ocr), the [Tesseract developer forum](https://groups.google.com/d/forum/tesseract-dev) and [past issues](https://github.com/tesseract-ocr/tesseract/issues), and if you still can't find what you need, ask for support in the mailing-lists.