create a brief post announcing the "Inside Rust" blog

I've dated it for tomorrow, since I don't plan to post it today.

Author: nikomatsakis

posts/2019-10-03-inside-rust-blog.md

@@ -0,0 +1,15 @@
+---
+layout: post
+title: "Announcing the Inside Rust blog"
+author: Niko Matsakis
+release: true
+---
+
+Today we're happy to announce that we're starting a second blog, the
+[**Inside Rust** blog][irb]. This blog will be used to post regular
+updates by the various Rust teams and working groups. If you're
+interested in following along with the "nitty gritty" of Rust
+development, then you should take a look!
+
+[irb]: /inside-rust/index.html
+