refine Spec

docs/proposals/formatted-output.md

@@ -25,7 +25,7 @@ The formatted output is not intended to supersede the prettified human-readable
 
 ORAS allows to use `--output` to output a file or directory in the filesystem. To enable users to format the metadata output of ORAS commands and compute figures based on the formatted output, these two options are proposed as follows:
 
-- Use `--format json|tree|table|go-template=GO_TEMPLATE` to format metadata output of ORAS commands into different formats including prettified JSON, tree, table view, and Go template. It supports computing figures within the template using [Sprig](http://masterminds.github.io/sprig/) functions. This is the primary and recommended usage.
+- Use `--format <DATA_FORMAT>` to format metadata output of ORAS commands into different formats including prettified JSON, tree, table view, and Go template, i.e. `--format json|tree|table|go-template=GO_TEMPLATE`. It supports computing figures within the template using [Sprig](http://masterminds.github.io/sprig/) functions. This is the primary and recommended usage.
 - Use `--template GO_TEMPLATE` to compute and manipulate the output data using Go template based on the chosen data format. To avoid ambiguous, this flag can only be used along with `--format <DATA_FORMAT>`.
 
 ## Feature status