test directive can appear anywhere in the file

Author: tshepang

src/tests/directives.md

@@ -6,7 +6,8 @@
 FIXME(jieyouxu) completely revise this chapter.
 -->
 
-Directives are special comments that tell compiletest how to build and interpret a test. They must appear before the Rust source in the test. They may also appear in `rmake.rs` [run-make tests](compiletest.md#run-make-tests).
+Directives are special comments that tell compiletest how to build and interpret a test.
+They may also appear in `rmake.rs` [run-make tests](compiletest.md#run-make-tests).
 
 They are normally put after the short comment that explains the point of this
 test. Compiletest test suites use `//@` to signal that a comment is a directive.