o: add page (#15888)

pages/common/o.md

@@ -0,0 +1,20 @@
+# o
+
+> Orbiton, a simple configuration-free text editor.
+> More information: <https://github.com/xyproto/orbiton>.
+
+- Open a file in editor:
+
+`o {{path/to/file}}`
+
+- Open a file as read-only:
+
+`o {{[-m|-monitor]}} {{path/to/file}}`
+
+- Save the file:
+
+`<Ctrl s>`
+
+- Quit Orbiton:
+
+`<Ctrl q>`