Fix readme after makefile -> justfile transition

Author: franeklubi

README.md

@@ -113,21 +113,25 @@ The source comprises two parts:
 - the `src/ast/*` generated by `tools/generate_ast.py`
 - the rest
 
-To get a release build just use `make`:
+To get a release build you can use `just`:
 ```sh
-$ make
+$ just
+```
+Or use cargo:
+```sh
+$ cargo build --release --verbose
 ```
 
 There are also a couple of useful dev commands like:
 ```sh
 # run REPL in watch mode
-$ make watch
+$ just watch
 
 # run the `sample_program.lux` in watch mode
-# (script source overridable with sample_program_path in makefile)
-$ make watch_sample
+# (script source overridable with sample_program_path in justfile)
+$ just watch_sample
 
 # run the `generate_ast.py` script with mypy checks in watch mode
-# (script source overridable with generate_ast_path in makefile)
-$ make watch_generate_ast
+# (script source overridable with generate_ast_path in justfile)
+$ just watch_generate_ast
 ```