Add long diagnostic for E0067

Author: caipre

src/librustc_typeck/diagnostics.rs

@@ -34,6 +34,25 @@ let x_is_nonzero = x as bool;
 ```
 "##,
 
+E0067: r##"
+The left-hand side of an assignment operator must be an lvalue expression. An
+lvalue expression represents a memory location and includes item paths (ie,
+namespaced variables), dereferences, indexing expressions, and field references.
+
+```
+use std::collections::LinkedList;
+
+// Good
+let mut list = LinkedList::new();
+
+
+// Bad: assignment to non-lvalue expression
+LinkedList::new() += 1;
+```
+
+```
+"##,
+
 E0081: r##"
 Enum discriminants are used to differentiate enum variants stored in memory.
 This error indicates that the same value was used for two or more variants,
@@ -139,7 +158,6 @@ register_diagnostics! {
     E0062,
     E0063,
     E0066,
-    E0067,
     E0068,
     E0069,
     E0070,