cmd/cue: update the list of output formats

This list was missing "cue" at the very least, since the playground
has supported it since day one.

Looking at internal/filetypes/types.go, more are likely missing.
For now, add another easy one, "binary".
Leave a TODO behind as a reminder to look at this again.

While here, right-align the format names to help readability,
especially since we'll at some point need to add longer names too.

Fixes #2186.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: Icc333c9d0c7c4344907eecd517d7bda712802847
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1168436
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>

cmd/cue/cmd/export.go

@@ -77,18 +77,25 @@ defined by the files in the current directory.
 
 
 Formats
+
 The following formats are recognized:
 
-json    output as JSON
-               Outputs any CUE value.
+    cue  output as CUE
+              Outputs any CUE value.
 
-text    output as raw text
-                The evaluated value must be of type string.
+   json  output as JSON
+              Outputs any CUE value.
 
-yaml    output as YAML
-                Outputs any CUE value.
-`,
+   yaml  output as YAML
+              Outputs any CUE value.
 
+   text  output as raw text
+              The evaluated value must be of type string.
+
+ binary  output as raw binary
+              The evaluated value must be of type string or bytes.
+`,
+		// TODO: some formats are missing for sure, like "jsonl" or "textproto" from internal/filetypes/types.cue.
 		RunE: mkRunE(c, runExport),
 	}