add links to rfcs, tracking issue

Author: nikomatsakis

text/2930-read-buf.md

@@ -1,7 +1,7 @@
 - Feature Name: read_buf
 - Start Date: 2020/05/18
-- RFC PR: [rust-lang/rfcs#0000](https://github.com/rust-lang/rfcs/pull/0000)
-- Rust Issue: [rust-lang/rust#0000](https://github.com/rust-lang/rust/issues/0000)
+- RFC PR: [rust-lang/rfcs#2930](https://github.com/rust-lang/rfcs/pull/2930)
+- Rust Issue: [rust-lang/rust#78485](https://github.com/rust-lang/rust/issues/78485)
 
 # Summary
 [summary]: #summary