Update the issues template (#507)

- Add a separator between checkboxes/details and issues list for avoiding removing (take a look to #503 and #504).
- Add Arc version (idea from #504).
- Avoid duplicity with GNOME Shell version (normally is the same as GTK+).
- Common issues:
  - Add AUR package building.
  - Add non-CSD apps transparency.
  - Add compiling with wrong GTK+ 3 version.
  - Be more clearer in others
  - Add a bit emphasis

* Fix english tense and a bunch of little fixes ->

- Put GTK+ 2 down, for making any order.
- XFCE notifications are already fixed.

* Do not force Markdown styling on details section

* Make the 3 first lines of this file clearer

* Clearer-est text

* Do not take care of old Arc version issues - Fix typo

.github/ISSUE_TEMPLATE.md

@@ -1,27 +1,33 @@
-**This list was created for avoiding duplicated issues, please read this before posting. If yours isn't listed here, delete this and continue.**
+### Please read this before posting:
 
-- The theme doesn't work in [distro] that doesn't have a GTK+ 3 version higher or equal than 3.14.
-  - Arc does not support version lower than 3.14, sorry.
-- The theme is broken after a GTK update.
-  - Recompile the theme.
+**This list was created for avoiding duplicated issues, if yours isn't listed, delete and continue.**
+
+- The theme doesn't work in [distro] that have a GTK+ 3 version lower than 3.14 (i.e. Linux Mint 17.x).
+  - Arc *only supports versions higher or equal than* 3.14.
+- The theme is broken after a major GTK+ 3 update (i.e. 3.18 :point_right: 3.20).
+  - Update the package or install from sources.
 - The theme is broken after installing from a repository.
-  - Check if the repository that you're using is specifically for the distribution (and distribution/GTK version) that you're using.
-- Using XFCE, the notifications looks ugly or are always full.
-  - Please check if Arc is the theme selected on the Notifications configuration.
-- GTK 2 theme looks like Windows 95 and LibreOffice/others looks ugly.
-  - Check if you have the Murrine GTK engine and `gnome-themes-standard` installed.
-- My GTK apps have a transparent background in Ubuntu.
+  - Check if the repository that you're using is *specifically* for the distribution (and distribution/GTK version) that you're using.
+- The theme is broken after installing from sources.
+  - Possibly a bug on GTK+ 3 version checking, use `--with-gnome=<version>` flag with `./autogen.sh`.
+- Theme isn't transparent on GNOME applications without CSD (i.e. Ubuntu's patched Nautilus).
+  - Transparency on GTK+ 3 themes *isn't supported* for non-CSD applications.
+- Theme doesn't build from AUR in Arch/Manjaro and others.
+  - Ensure you have the `base-devel` group installed.
+- Some GTK+ 3 applications have a transparent background in Ubuntu.
   - Run this in terminal: `gsettings set com.canonical.desktop.interface scrollbar-mode normal`.
+- GTK+ 2 theme looks like Windows 95 and LibreOffice/others looks ugly.
+  - Check if you have the Murrine GTK engine and `gnome-themes-standard` installed.
 
-**Mark those:**
+----
 
 - [ ] I read the list above.
 - [ ] I read the README.
-- [ ] I've checked if my issue isn't duplicated.
+- [ ] I checked if my issue isn't duplicated.
 
-**And complete this:**
+**Details:**
 
 - Distribution:
 - Desktop environment:
 - GTK+ 3 version:
-- GNOME Shell version (if using):
+- Arc version (commit):