Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Please read the [wiki](https://github.com/lcpz/lain/wiki) and browse the [Issues section](https://github.com/lcpz/lain/issues) first.**
+
+If you can't find a solution, then please provide:
+
+* output of `awesome -v` and `lua -v`
+* expected behavior and actual behavior
+* steps to reproduce the problem
+* X error log
+
+### How to provide X error log
+
+There are two ways:
+
+* (Physically) Restart X like this:
+  ```shell
+  startx -- -keeptty -nolisten tcp > $HOME/.xorg.log 2>&1
+  ```
+  the error log will be output into `$HOME/.xorg.log`.
+
+* (Virtually) Use [Xephyr](https://wikipedia.org/wiki/Xephyr):
+  ```shell
+  # set screen size as you like
+  Xephyr :1 -screen 1280x800 2> stdout.txt & DISPLAY=:1 awesome
+  ```
+  the error log will be output in the file `stdout.txt`.
+
+Before reporting, read the log and see if you can solve it yourself.