ISSUE_TEMPLATE: add request to share crash.log (#3296)

.github/ISSUE_TEMPLATE.md

@@ -5,3 +5,18 @@
 #### Issue
 
 #### Steps to reproduce
+
+##### `crash.log` (if applicable)
+`crash.log` is a file that is automatically created when KOReader crashes. It can
+normally be found in the KOReader directory:
+
+* `koreader/` directory for Kindle
+* `.adds/koreader/` directory for Kobo
+* `applications/koreader/` directory for Pocketbook
+
+Please try to include the relevant sections in your issue description.
+You can upload the whole `crash.log` file on GitHub by dragging and
+dropping it onto this textbox, or you can use one of these paste services.
+Please don't forget to set a high expiration date if you do.
+https://pastebin.com https://slexy.org https://paste2.org https://fpaste.org
+http://ix.io https://paste.kde.org https://paste.debian.net.