README.md: oot config: discuss build dir contents

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/README.md b/README.md
index 520f7ebf30f229186334b2f057e1f25649a5ad11..02dede042dd2a7d85744f37c8570ca068018d49d 100644 (file)
--- a/README.md
+++ b/README.md
@@ -302,6 +302,11 @@ To control use of alternative `Cargo.lock` filename, use the section
    parent of the invocation directory (and could be a symlink then).
    Default is `Build` (assuming `use` is specified).
 
+   The build directory will contain one subdir for each package: each
+   subdir in the build dir corresponds to one source dir where
+   nailing-cargo was invoked.  nailing-cargo will arrange to create
+   these subdirectories, so the build directory can start out empty.
+
   * `use`: How to become the build user.  Needs to be combined
     with other setting(s):