man: Document the working directory when running dpkg-buildpackage hooks

debian/changelog

@@ -1,5 +1,10 @@
 dpkg (1.18.16) UNRELEASED; urgency=medium
 
+  [ Guillem Jover ]
+  * Documentation:
+    - State the current working directory used when running dpkg-buildpackage
+      hooks.
+
   [ Updated scripts translations ]
   * German (Helge Kreutzmann).
 

man/dpkg-buildpackage.man

@@ -341,6 +341,7 @@ which will run at the times specified in the run steps (since dpkg 1.17.6).
 The hooks will
 always be executed even if the following action is not performed (except
 for the \fBbinary\fP hook).
+All the hooks will run in the unpacked source directory.
 
 Note: Hooks can affect the build process, and cause build failures if
 their commands fail, so watch out for unintended consequences.