agg: add --cols,--rows, --help examples (#18232)

agg: add examples

Author: nelsonfigueroa

pages/common/agg.md

@@ -6,3 +6,11 @@
 - Create a GIF:
 
 `agg {{path/to/demo.cast}} {{path/to/demo.gif}}`
+
+- Create a GIF that is 80 columns wide and 25 rows in height:
+
+`agg --cols 80 --rows 25 {{path/to/demo.cast}} {{path/to/demo.gif}}`
+
+- Display help:
+
+`agg {{[-h|--help]}}`