Deprecate the nu_scripts version of stdlib-candidate (#1042)

Deprecates the existing `stdlib-candidate` directories in `nu_scripts`
since `std-rfc` has now transitioned to the main repo. Updates readme
and renamed directories.

stdlib-candidate-archive/stdlib-candidate-older/std-rfc/mod.nu

@@ -0,0 +1,12 @@
+# Modules
+export module record/
+export module str/
+export module math/
+
+# Commands
+export use bulk-rename.nu *
+export use set-env.nu *
+export use bench.nu
+export use script-parsing.nu [ parse-arg ]
+export use conversions *
+export use tables *