Minor fix README.md (#219)

Author: udesou

README.md

@@ -33,17 +33,14 @@ The directory structure should look like the diagram below:
 ```
 Your working directory/
 ├─ mmtk-julia/
-│  ├─ julia/
 │  └─ mmtk/
 ├─ julia/ (should be cloned manually)
 └─ mmtk-core/ (optional)
 ```
 
 #### Build Julia binding in Rust
 
-Before building Julia, build the binding in `mmtk-julia`. Set `MMTK_JULIA_DIR` to the absolute path containing the binding's top-level directory and build the binding by running `make release` or `make debug` from that directory.
-
-We currently only support a (non-moving) Immix implementation. We hope to add support for non-moving StickyImmix and the respective moving versions of both collectors in the near future. We also only support x86_64 Linux, more architectures should also be supported in the near future.
+Before building Julia, set `MMTK_JULIA_DIR` to the absolute path containing the binding's top-level directory. Run `make -C $MMTK_JULIA_DIR clean` to make sure you have a fresh version of the binding, and to force it to be built when building Julia. We currently only support a (non-moving) Immix implementation. We hope to add support for non-moving StickyImmix and the respective moving versions of both collectors in the near future. We also only support x86_64 Linux, more architectures should also be supported in the near future.
 For a release build with debugging information, first add `debug = true` under `[profile.release]` in `mmtk/Cargo.toml`.
 Make sure you have the prerequisites for building [MMTk](https://github.com/mmtk/mmtk-core#requirements).
 
@@ -67,7 +64,7 @@ export MMTK_JULIA_DIR := <path-to-mmtk-julia>
 export MMTK_PLAN := Immix
 ```
 
-If you have done a debug build of the binding, make sure to also set `MMTK_BUILD=debug` before building Julia.
+If you would like to do a debug build of the binding, make sure to also set `MMTK_BUILD=debug` before building Julia.
 
 ### Rust FFI bindings from Julia