clarify readme

README.md

@@ -22,7 +22,8 @@ To a conf file (probably local.conf)
 
 ### What about cargo?:
 
-We provide .bb files for these, and they are working every now-and-then.
+We provide .bb files for cargo (-target) and cargo-native, and they are working
+every now-and-then.
 Unfortunately, rust moves a bit too quickly for cargo to keep up, and it ends
 up broken fairly often.
 
@@ -30,6 +31,8 @@ Very often we'll want newer versions of rust than cargo is able to build with.
 Thankfully, we don't need any custom cargo configuration, and can use a vanilla
 cargo binary.
 
+We add "cargo-native" to ASSUME_PROVIDED unless overridden by clearing CARGO_PROVIDED (via conf/layer.conf)
+
 ## What's untested:
 
  - rust (built for target)