Add local build instructions to the README

README.md

@@ -8,9 +8,43 @@ This repository holds the [MMTk](https://www.mmtk.io/) bindings for Ruby. The bi
 
 Since this repository is sync'd into [ruby/ruby](https://github.com/ruby/ruby/), you can choose to either build it in this repository or build it in ruby/ruby. If you're building it in this repository, note that it is only expected to work on the latest commit of Ruby master.
 
-1. Build Ruby by following the [Building Ruby](https://docs.ruby-lang.org/en/master/contributing/building_ruby_md.html) guide, but append `--with-shared-gc=<dir>` when configuring. `dir` will be the directory that the compiled GC implementations will be placed in.
+To build `librubygc.mmtk.so` locally, run the following:
+
+```sh
+  rake compile
+```
+This command will:
+
+   - **Clone the Ruby repository**: If you don't already have it, the script clones Ruby into `res/ruby`.
+   - **Copy MMTk GC code**: It copies the MMTk garbage collector code into the Ruby source tree.
+   - **Configure and build Ruby**: Sets up the build configurations to integrate MMTk with Ruby's garbage collector API.
+   - **Compiling the MMTk shared library**: Builds `librubygc.mmtk.so` using Rust's Cargo build system.
+   - **Install the shared library**: Copies `librubygc.mmtk.so` into the `mod_gc` directory.
+
+Once it's done, you'll have a shared object `mod_gc/librubygc.mmtk.so` (`modgc/librubygc.mmtk.bundle` on macOS), that can be loaded into any Ruby interpeter built `--with-shared-gc` support. 
+
+Successful builds, when loaded, will display `+GC[mmtk]`  in the Ruby version string. This indicates that Ruby has been compiled with shared GC support and that MMTk is loaded.
+
+```sh
+  RUBY_GC_LIBRARY=mmtk ruby -v
+  ruby 3.4.0dev (2024-11-25T13:05:23Z master f127bcb829) +PRISM +GC[mmtk] [arm64-darwin24]
+```
+
+**Note**: Make sure you have all the necessary dependencies installed:
+
+- **Rust toolchain**: Required for building MMTk.
+- **Ruby build dependencies**: Libraries and tools needed to compile Ruby from source.
+- **Rake**: Ruby's build program, used to run the compile task.
+
+That's it! You're all set to experiment with different GC algorithms in Ruby using MMTk.
+
+
+
+
+
+
+
 
-TODO: rest of the building guide
 
 ### Running