doc: improve E0133 explanation

Author: tshepang

src/librustc/diagnostics.rs

@@ -731,9 +731,14 @@ type X = u32; // ok!
 "##,
 
 E0133: r##"
-Using unsafe functionality, such as dereferencing raw pointers and calling
-functions via FFI or marked as unsafe, is potentially dangerous and disallowed
-by safety checks. These safety checks can be relaxed for a section of the code
+Using unsafe functionality, is potentially dangerous and disallowed
+by safety checks. Examples:
+
+- Dereferencing raw pointers
+- Calling functions via FFI
+- Calling functions marked unsafe
+
+These safety checks can be relaxed for a section of the code
 by wrapping the unsafe instructions with an `unsafe` block. For instance:
 
 ```