readme: multiple versions of packages dont work with SRCDIR

Author: cirosantilli

README.adoc

@@ -5248,6 +5248,26 @@ and now you can see that a new version of `kernel_module` was built and put insi
 ls out/x86_64/buildroot/build/kernel_module-mybranch
 ....
 
+TODO: is there a way to do it nicely for `*_OVERRIDE_SRCDIR` packages from link:buildroot_override[]? I tried:
+
+....
+./build -l LINUX_VERSION=mybranch
+....
+
+but it fails with:
+
+....
+linux/linux.mk:492: *** LINUX_SITE cannot be empty when LINUX_SOURCE is not.  Stop.
+....
+
+and theI tried:
+
+....
+./build -l LINUX_VERSION=mybranch LINUX_SITE="$(pwd)/linux"
+....
+
+but it feels hack-ish, and the build was slower than normal, looks like the build was single threaded?
+
 === BR2_TARGET_ROOTFS_EXT2_SIZE
 
 When adding new large package to the Buildroot root filesystem, it may fail with the message: