Added README file

README

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+Software Installation Tool (SIT)
+--------------------------------
+
+SIT is a simple software installation tool inspired by gentoo's emerge script.
+It eases the installation process and helps to prevent errors during the 
+installation as well as helps with the documentation as it generates a lot of
+log files and installes them together with the softwre package.
+
+In its current version it can only install a package using a package class file
+including the necessary information
+
+The package tree resides per default in the directory $SITi_PATH/packages. For
+convenience it should look like following
+  $SIT_PATH/packages/CATEGORY/PACKAGE-VERSION
+
+
+The global configuration file of SIT is $SIT_PATH/etc/sit.conf
+It includes a variety of default values:
+PREFIX_BASE
+SRC_POOL     
+SCLASS_DIR
+
+The installation process is currently controled with the following environment 
+variables:
+* COMPILER
+* COMPILER_VERSION
+* MPI
+* MPI_VERSION
+
+
+To install a package simply call sit with the necessary information provided by 
+these variables:
+> [VARIABLE_DECLARATIONS] sit PACKAGE
+
+e.g.
+
+> PREFIX_BASE=/opt COMPILER=gnu COMPILER_VERSION=4.5 sit mpi/openmpi-1.5.1
+
+
+
+PACKAGE FILES:
+
+Package files should include all the necessary information for the installation
+proces. The syntax of the package class files is inspired by gentoo's ebuild files.
+
+
+A sit package file must contain at least the following variables
+
+A   archive (source tarball)
+P   package (name of extracted source folder)
+URL
+INSTALLER
+
+
+Optional varialbes to control the build process are
+
+CONFIGURE_OPTS  options which will be passed to configure
+MAKEOPTS        options which will be passed to make (see sit.conf)
+
+
+During the installation the following directory paths are used
+WORKDIR         working directory to which e.g. sources will be unpacked
+SRCDIR          source directory
+BUILDDIR        directory in which the package will be build ($SRCDIR/build)
+LOGDIR          directory storing the temporary logfiles ($WORKDIR)
+
+
+For fine tuning of the installation process the user can overwrite the following 
+functions. If not other mentioned they are executed in $BUILDDIR
+
+src_unpack      extract $SRC_POOL/${A} into $WORKDIR
+src_configure   configure
+src_build       make
+src_pretest     
+src_install     make install
+src_posttest
+
+
+The following helper functions can be used 
+
+unpack      recognize and extract a compressed tar file
+
+
+