Documented the build process in README

README.md

@@ -1,8 +1,35 @@
 # SystemRescueCd
 
-## SystemRescueCd project
+## Project website
 Homepage: http://www.system-rescue-cd.org/
 
-## SystemRescueCd sources
+## Project sources
 This git repository contains SystemRescueCd sources files. This is based on
 https://git.archlinux.org/archiso.git
+
+## Building SystemRescueCd
+SystemRescueCd can be built for x86_64 or i686 architectures. It must be built
+on archlinux (or archlinux32). The following packages must be installed on the
+build system: archiso, grub, mtools. The archiso package must be modified to add
+support for an option which allows to optimize the squashfs compression. The
+patch can be found in the "patches" folder in this git repository.
+
+The package list contains packages which are not part of the official binary
+package repositories. These packages need to be built from sources from the AUR
+website. These sources are made of at least a PKGBUILD file and quite often
+other related files, such as patches. These can be built using the makepkg
+command which generates binary packages. These binary packages must be copied to
+a custom package repository which can be hosted locally using httpd or nginx.
+The repo-add command must be used to generate the repository package index.
+The pacman.conf file must be updated with the address of this repository so
+custom packages can be accessed.
+
+By default the target architecture will be x86_64. The following must be changed
+in order to build a 32bit version instead:
+* Update the ARCHITECTURE file (replace "x86_64" with "i686")
+* Update Architecture in pacman.conf (replace "auto" with "i686")
+* Replace archlinux repositories with archlinux32 repositories in pacman.conf
+
+The build process can be started by running the build.sh script. It will create
+a large "work" sub-directory and the ISO file will be written in the "out"
+sub-directory.