Update intro.md

Very dumb PR/fix but type punning -> pinning . Nothing funny about types!

src/intro.md

@@ -35,7 +35,7 @@ The Reference will tell you the syntax and semantics of references, destructors,
 It should be noted that we haven't synced The Rustnomicon and The Reference well, so they may have a duplicate content.
 In general, if the two documents disagree, The Reference should be assumed to be correct (it isn't yet considered normative, it's just better maintained).
 
-Topics that are within the scope of this book include: the meaning of (un)safety, unsafe primitives provided by the language and standard library, techniques for creating safe abstractions with those unsafe primitives, subtyping and variance, exception-safety (panic/unwind-safety), working with uninitialized memory, type punning, concurrency, interoperating with other languages (FFI), optimization tricks, how constructs lower to compiler/OS/hardware primitives, how to **not** make the memory model people angry, how you're **going** to make the memory model people angry, and more.
+Topics that are within the scope of this book include: the meaning of (un)safety, unsafe primitives provided by the language and standard library, techniques for creating safe abstractions with those unsafe primitives, subtyping and variance, exception-safety (panic/unwind-safety), working with uninitialized memory, type pinning, concurrency, interoperating with other languages (FFI), optimization tricks, how constructs lower to compiler/OS/hardware primitives, how to **not** make the memory model people angry, how you're **going** to make the memory model people angry, and more.
 
 The Rustonomicon is not a place to exhaustively describe the semantics and guarantees of every single API in the standard library, nor is it a place to exhaustively describe every feature of Rust.