Move rustc docs to the book

This is super black magic internals at the moment, but having it
somewhere semi-public seems good. The current versions weren't being
rendered, and they'll be useful for some people.

Fixes #21281

Author: steveklabnik

src/doc/trpl/README.md

@@ -33,3 +33,7 @@ chapters focus on the most complex features, as well as some things that
 are only available in upcoming versions of Rust.
 
 After reading "Advanced," you'll be a Rust expert!
+
+<h2 class="section-header"><a href="internals.html">Internals</a></h2>
+
+This section is full of documentaion of compiler internals. Here be dragons.

src/doc/trpl/SUMMARY.md

@@ -1,6 +1,6 @@
 # Summary
 
-* [I: The Basics](basic.md)
+* [The Basics](basic.md)
     * [Installing Rust](installing-rust.md)
     * [Hello, world!](hello-world.md)
     * [Hello, Cargo!](hello-cargo.md)
@@ -15,7 +15,7 @@
     * [Arrays, Vectors, and Slices](arrays-vectors-and-slices.md)
     * [Standard Input](standard-input.md)
     * [Guessing Game](guessing-game.md)
-* [II: Intermediate Rust](intermediate.md)
+* [Intermediate Rust](intermediate.md)
     * [More Strings](more-strings.md)
     * [Crates and Modules](crates-and-modules.md)
     * [Testing](testing.md)
@@ -31,9 +31,16 @@
     * [Concurrency](concurrency.md)
     * [Error Handling](error-handling.md)
     * [Documentation](documentation.md)
-* [III: Advanced Topics](advanced.md)
+* [Advanced Topics](advanced.md)
     * [FFI](ffi.md)
     * [Unsafe Code](unsafe.md)
     * [Macros](macros.md)
     * [Compiler Plugins](plugins.md)
+* [Compiler Internals](internals.md)
+    * [Borrow Checker](borrow-checker.md)
+    * [Trait Resolution](trait-resolution.md)
+    * [Inference](inference.md)
+    * [Higher Ranked Items](higher-ranked-items.md)
+    * [Region Inference](region-inference.md)
+    * [Method Lookup](method-lookup.md)
 * [Conclusion](conclusion.md)