Updated README.md usage info

README.md

@@ -36,8 +36,10 @@ Use the following keys to control sxiv:
     Escape       Quit sxiv and return an exit value of 2 (useful for scripting)
     Space,n      Go to the next image
     Backspace,p  Go to the previous image
-		g/G          Go to first/last image
-		[/]          Go 10 images backward/forward
+    g/G          Go to first/last image
+    [/]          Go 10 images backward/forward
     +,=          Zoom in
     -            Zoom out
     h,j,k,l      Scroll left/down/up/right
+    f            Toggle fullscreen mode (requires an EWMH/NetWM compliant
+                 window manager)