crane/gcrane: add pages (#13853)

pages/common/crane-export.md

@@ -0,0 +1,16 @@
+# crane export
+
+> Export filesystem of a container image as a tarball.
+> More information: <https://github.com/google/go-containerregistry/blob/main/cmd/crane/doc/crane_digest.md>.
+
+- Write tarball to stdout:
+
+`crane export {{image_name}} -`
+
+- Write tarball to file:
+
+`crane export {{image_name}} {{path/to/tarball}}`
+
+- Read image from stdin:
+
+`crane export - {{path/to/filename}}`