github: ask for arch+kernel in bug report form

Quite often we see kernel and arch specific issues, let's ask for the
version right-away when people file the issue.

Other tweaks.

.github/ISSUE_TEMPLATE/Bug_report.md

@@ -5,7 +5,7 @@ about: A report of an error in a recent systemd version
 ---
 
 **systemd version the issue has been seen with**
-> ...
+ > …
 
 <!-- **NOTE:** Do not submit bug reports about anything but the two most recently released (non-rc) systemd versions upstream! -->
 <!-- See https://github.com/systemd/systemd/releases for the list of most recent releases. -->
@@ -14,6 +14,12 @@ about: A report of an error in a recent systemd version
 **Used distribution**
  > …
 
+**Linux kernel version used** (`uname -a`)
+ > …
+
+**CPU architecture issue was seen on**
+ > …
+
 **Expected behaviour you didn't see**
  > …
 
@@ -21,3 +27,4 @@ about: A report of an error in a recent systemd version
  > …
 
 **Steps to reproduce the problem**
+ > …