README: document trouble with tricky packages, and submodules

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

diff --git a/README.md b/README.md
index 0df1f9409a127add823b3da2482307020a203ee4..25122c565f62b63574dd36fbc392ee676f9f3069 100644 (file)
--- a/README.md
+++ b/README.md
@@ -748,6 +748,19 @@ Limitations and bugs
     with `Cargo.nail` files which imply overlapping sets of package
     directories, things will go Badly Wrong.
 
+  * Many real-world packages do not support out-of-tree builds
+    properly.  Doing so well is not easy because cargo does not
+    provide a package with all the path information needed to do a
+    good job.  Also the Rust community's infrastructure and tooling
+    does not do out-of-tree builds by default.
+
+    If you encounter such a package, `--linkfarm` will often help.
+
+  * git submodules are not supported.  In theory this could perhaps be
+    improved, but it is not trivial because git submodules are badly
+    broken.  If you can, avoid git submodule and use other techniques
+    instead (e.g., `git subtree`).
+
 Contributing and legal
 ======================