Add a README.md for lib/obj.

lib/obj/Cargo.toml

@@ -2,10 +2,12 @@
 name = "wasmtime-obj"
 version = "0.0.0"
 authors = ["The Cranelift Project Developers"]
+description = "Native object file output for WebAsssembly code in Wasmtime"
 publish = false
 repository = "https://github.com/CraneStation/wasmtime"
 categories = ["wasm"]
 license = "Apache-2.0 WITH LLVM-exception"
+readme = "README.md"
 
 [dependencies]
 cranelift-codegen = "0.25.0"

lib/obj/README.md

@@ -0,0 +1,6 @@
+This is the `wasmtime-obj` crate, which contains an experimental prototype
+for writing out native object files, using the wasm ABI defined by
+[`wasmtime-environ`].
+
+[`wasmtime-environ`]: https://crates.io/crates/wasmtime-environ
+