📝 Add formatter info to README

README.md

@@ -123,7 +123,15 @@ Each separate output has its own set of configuration. So, replace `which-one` w
 
 *This section may change in the near future. We're considering supporting multiple formats.*
 
-- `json`: Outputs as JSON
+- `formatter`: Which formatter to use when outputting data. This value is used by `my-log drop` to output the new entry.
+
+### `[formatters]`
+
+Some formatters may have custom configuration.
+
+#### `[formatters.json]`
+
+- `pretty_print`: If true, JSON output will be pretty printed. If false, it will be printed to a single line.
 
 ## Roadmap