auto merge of #11764 : Armavica/rust/doc_patmatch, r=pcwalton

I also removed the obsolete '*' wildcard from the manual.

doc/tutorial.md

@@ -520,6 +520,16 @@ to the value of the matched value inside of the arm's action. Thus, `(0.0,
 y)` matches any tuple whose first element is zero, and binds `y` to
 the second element. `(x, y)` matches any two-element tuple, and binds both
 elements to variables.
+A subpattern can also be bound to a variable, using `variable @ pattern`. For
+example:
+
+~~~~
+# let age = 23;
+match age {
+    a @ 0..20 => println!("{} years old", a),
+    _ => println!("older than 21")
+}
+~~~~
 
 Any `match` arm can have a guard clause (written `if EXPR`), called a
 *pattern guard*, which is an expression of type `bool` that