psx_build : updated readme

Author: 50thomatoes50

PSXToolchain/README.md

@@ -5,6 +5,8 @@ In order to start building a Playstation version of **REDRIVER2** you'll need to
  - Put **mipsel-unknown-elf** toolchain to this folder (https://github.com/majenkotech/mipsel-unknown-elf/releases)
  - Install **make**
  - Obtain **Psy-Q SDK** converted for *latest GCC*
+ - Copy (https://github.com/pcsx-redux/nugget/tree/main/common) to `/PSXToolchain/PsyQ/common`
  - Execute **psx_build.bat**
+ - Install [mkpsxiso](https://github.com/Lameguy64/mkpsxiso/releases)
  - Execute **psx_makecd.bat**
  - Locate and use **CDSrc/REDRIVER2.bin** and **cue** files