Add grid output option to USAGE.md

src/docs/USAGE.md

@@ -124,6 +124,7 @@ List of available formats to use with the _output_ option:
 | md       | A Markdown format |
 | ch       | An OpenAF channel format |
 | chart    | A line-chart like chart (usefull together with 'loop') |
+| grid     | A multiple output ascii grid (usefull together with 'loop') |
 | mdtable  | A Markdown table format (only for list outputs) |
 | openmetrics | Converts a map or list to OpenMetrics/Prometheus compatible format |
 | base64   | A base64 text format | 
@@ -346,6 +347,16 @@ List of options to use when _out=chart_:
 
 ---
 
+## 🧾 Grid output options
+
+List of options to use when _out=grid_:
+
+| Option | Type | Description |
+|--------|------|-------------|
+| grid   | String | A JSON/SLON configuration composed of an array with another array per grid line. Each line array should have a map per column. Each map should be composed of a 'title', a 'type' (tree, map, chart, bar, table, area, text and md), a 'path' to select the data (for non chart types) and an 'obj' (for chart type the format is the same of chart=...) |
+
+---
+
 ## 🧾 XLS output options
 
 List of options to use when _out=xls_: