Updated documentation

Author: piranna

README.md

@@ -5,10 +5,11 @@
 This package generate a cross-compiler based on [gcc](https://gcc.gnu.org/) and
 [musl](musl-libc.org) ready to use on the NodeOS build system, but could be used
 by other systems. You can be able to configure the target of the cross-compiler
-by setting some optional environment variables:
+by setting some optional build flags or environment variables:
 
-- **PLATFORM**: by default it will generate for the current system
-- **CPU**: by default it will generate for the current CPU
+- **-b**/**BITS**: select between x86 or x86_64
+- **-c**/**CPU**: by default it will generate for the current CPU
+- **-M**/**MACHINE**: target machine according QEmu definitions
 
 This `bin` folder contain placeholders for `npm` during the install step. They
-will be replaced later during the install process to their correct symlinks.
+are being replaced later during the install process to their correct symlinks.