chore(just) Rename the target rust to build.

Author: Hywan

README.md

@@ -263,7 +263,7 @@ This function returns a boolean.
 To compile the entire project, run the following commands:
 
 ```sh
-$ just rust
+$ just build
 $ just test
 $ ruby examples/simple.rb
 ```

justfile

@@ -1,5 +1,5 @@
-# Compile and install the Rust library.
-rust:
+# Compile and install the Ruby extension.
+build:
 	rake build_lib
 
 # Run the tests.