Add the missing ramble docs command

It simply opens up the doc page, same as what Spack does.

lib/ramble/ramble/cmd/docs.py

@@ -0,0 +1,17 @@
+# Copyright 2022-2024 The Ramble Authors
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+import webbrowser
+
+description = "open Ramble documentation in a web browser"
+section = "help"
+level = "short"
+
+
+def docs(parser, args):
+    webbrowser.open("https://ramble.readthedocs.io/")

lib/ramble/ramble/main.py

@@ -295,7 +295,7 @@ def add_subcommand_group(title, commands):
   ramble help --all       list all commands and options
   ramble help <command>   help on a specific command
   ramble help --spec      help on the application specification syntax
-  ramble docs             open https://ramble.rtfd.io/ in a browser
+  ramble docs             open https://ramble.readthedocs.io/ in a browser
 """.format(
                 help=section_descriptions["help"]
             )