diff --git a/pw_package/docs.rst b/pw_package/docs.rst
index 24037e5..78d99b8 100644
--- a/pw_package/docs.rst
+++ b/pw_package/docs.rst
@@ -16,6 +16,13 @@
 * The dependency needs to be "installed" into the system in some manner beyond
   just extraction and thus isn't a good match for distribution with CIPD.
 
+Pigweed itself includes a number of packages that simply clone git repositories.
+In general, these should not be used by projects using Pigweed. Pigweed uses
+these packages to avoid using submodules so downstream projects don't have
+multiple copies of a given repository in their source tree. Projects using
+Pigweed should use submodules instead of packages because submodules are
+supported by much more mature tooling: git.
+
 -----
 Usage
 -----