Updated README file.

README

@@ -9,16 +9,19 @@ 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
+The package tree resides per default in the directory $SIT_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
+* PREFIX_BASE
+* SRC_POOL     
+* SCLASS_DIR
+
+* DEFAULT_PLATFORM
+* DEFAULT_COMPILER
 
 The installation process is currently controled with the following environment 
 variables:
@@ -26,6 +29,14 @@ variables:
 * COMPILER_VERSION
 * MPI
 * MPI_VERSION
+* HOSTNAME
+
+Sit detects currently the build platform using the HOSTNAME variable. If sit 
+cannot determine the PLATFORM it uses the default platform specified in sit.conf.
+For each platform configuration files are stored unter 
+  $SIT_PATH/etc/platform-configs/$PLATFORM/*
+
+At the moment only compiler configurations are supported.
 
 
 To install a package simply call sit with the necessary information provided by