pages*: mark keys according to the guideline (#11907)

pages/linux/i3.md

@@ -9,24 +9,24 @@
 
 - Open a new terminal window:
 
-`Super + Return`
+`<Super> + <Return>`
 
 - Create a new workspace:
 
-`Super + Shift + {{number}}`
+`<Super> + <Shift> + {{number}}`
 
 - Switch to workspace number `n`:
 
-`Super + {{n}}`
+`<Super> + {{n}}`
 
 - Open new window horizontally:
 
-`Super + h`
+`<Super> + h`
 
 - Open new window vertically:
 
-`Super + v`
+`<Super> + v`
 
 - Open application (type out application name after executing command):
 
-`Super + D`
+`<Super> + D`