gtop: add page (#1640)

pages/common/gtop.md

@@ -0,0 +1,15 @@
+# gtop
+
+> System monitoring dashboard for the terminal.
+
+- Show the system stats dashboard:
+
+`gtop`
+
+- Sort by CPU usage:
+
+`c`
+
+- Sort by memory usage:
+
+`m`