chore: improving error log for oras push and oras attach when the…

… annotation file is invalid (oras-project#1026)

Signed-off-by: Shubham Singh <shubhammahar1306@gmail.com>

cmd/oras/internal/option/packer.go

@@ -99,7 +99,13 @@ func (opts *Packer) LoadManifestAnnotations() (annotations map[string]map[string
 	}
 	if opts.AnnotationFilePath != "" {
 		if err = decodeJSON(opts.AnnotationFilePath, &annotations); err != nil {
-			return nil, err
+			errStr :=  err.Error()
+			docLink := " Please refer to the document at https://oras.land/docs/how_to_guides/manifest_annotations."
+			if !strings.HasSuffix(errStr, ".") {
+				docLink = "."+docLink
+			}
+			return nil, fmt.Errorf("failed to load annotations from %s: %w" +
+				docLink, opts.AnnotationFilePath, err)
 		}
 	}
 	if len(opts.ManifestAnnotations) != 0 {