RFC 2141: Add support to Cargo for alternative registries

Author: aturon

text/0000-alternative-registries.md renamed to text/2141-alternative-registries.md

@@ -1,7 +1,7 @@
 - Feature Name: cargo_alternative_registries
 - Start Date: 2017-09-06
-- RFC PR: (leave this empty)
-- Rust Issue: (leave this empty)
+- RFC PR: https://github.com/rust-lang/rfcs/pull/2141
+- Rust Issue: https://github.com/rust-lang/rust/issues/44931
 
 # Summary
 [summary]: #summary