add keymaps for quick filtering the test-listings

doc/test-samurai.txt

@@ -54,6 +54,9 @@ Additional keymaps:
   <leader>qn    Close floats + jump to the first quickfix entry
   <leader>nf    Next [ FAIL ] in listing
   <leader>pf    Previous [ FAIL ] in listing
+  <leader>sf    Filter listing to [ FAIL ] only
+  <leader>ss    Filter listing to [ SKIP ] only
+  <leader>sa    Show all listing entries (clear filter)
   <leader>o     Jump to test location
   <leader>z     Toggle Detail-Float full width
   <C-l>         Focus Detail-Float (press l again for full)