fix(tar): be more clear that we only support create mode

lib/private/tar.bzl

@@ -57,18 +57,19 @@ _tar_attrs = {
         doc = """A mode indicator from the following list, copied from the tar manpage:
 
        - create: Create a new archive containing the specified items.
-       - append: Like `create`, but new entries are appended to the archive.
-            Note that this only works on uncompressed archives stored in regular files.
-            The -f option is required.
-       - list: List  archive contents to stdout.
-       - update: Like `append`, but new entries are added only if they have a
-            modification date newer than the corresponding entry in the archive.
-	       Note that this only works on uncompressed archives stored in
-	       regular files. The -f option	is required.
-       - extract: Extract to disk from the archive. If a file with the same name
-	       appears more than once in the archive, each copy	 will  be  extracted,
-           with  later  copies  overwriting  (replacing) earlier copies.
-        """,
+
+       Other modes may be added in the future.""",
+        #    - append: Like `create`, but new entries are appended to the archive.
+        #         Note that this only works on uncompressed archives stored in regular files.
+        #         The -f option is required.
+        #    - list: List  archive contents to stdout.
+        #    - update: Like `append`, but new entries are added only if they have a
+        #         modification date newer than the corresponding entry in the archive.
+        #        Note that this only works on uncompressed archives stored in
+        #        regular files. The -f option	is required.
+        #    - extract: Extract to disk from the archive. If a file with the same name
+        #        appears more than once in the archive, each copy	 will  be  extracted,
+        #        with  later  copies  overwriting  (replacing) earlier copies.
         values = ["create"],  # TODO: support other modes: ["append", "list", "update", "extract"]
         default = "create",
     ),