Add copyright for boost build documentaiton.

Since there wasn't any copyright notice I should probably check with
Vladmir before comitting this one.

[SVN r63393]

tools/build

@@ -1 +1 @@
-Subproject commit 88cd187526ff5ffb285554232911664bd523bc5b
+Subproject commit 5d6c61ca0999fc7db816aef78b37fa557327a474