Update Readme.md

Author: GuillaumeGomez

Readme.md

@@ -21,6 +21,7 @@ You can also use my [fork of gcc](https://github.com/antoyo/gcc) which already i
 To build it (most of these instructions come from [here](https://gcc.gnu.org/onlinedocs/jit/internals/index.html), so don't hesitate to take a look there if you encounter an issue):
 
 ```bash
+$ git clone https://github.com/antoyo/gcc
 $ cd gcc
 $ ./contrib/download_prerequisites
 $ sudo apt install flex libmpfr-dev libgmp-dev libmpc3 libmpc-dev
@@ -31,23 +32,33 @@ $ ./configure \
    --enable-checking=release \
    --prefix=$(pwd)/install \
    --disable-multilib
+$ make -j4 # You can replace `4` with another number depending on how many cores you have.
+$ cd ..
 ```
 
 **Put the path to your custom build of libgccjit in the file `gcc_path`.**
 
 ```bash
-$ git clone https://github.com/rust-lang/rustc_codegen_gcc.git
-$ cd rustc_codegen_gcc
+$ dirname $(readlink -f `find . -name libgccjit.so`) > gcc_path
+```
+
+You can set also set RUST_COMPILER_RT_ROOT:
+
+```bash
 $ git clone https://github.com/llvm/llvm-project llvm --depth 1 --single-branch
 $ export RUST_COMPILER_RT_ROOT="$PWD/llvm/compiler-rt"
-$ ./prepare_build.sh # download and patch sysroot src
-$ ./build.sh --release
 ```
 
-To run the tests:
+Then you can run commands like this:
 
 ```bash
 $ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
+$ LIBRARY_PATH=$(cat gcc_path) LD_LIBRARY_PATH=$(cat gcc_path) ./build.sh --release
+```
+
+To run the tests:
+
+```bash
 $ ./test.sh --release
 ```