updated readme

README.md

@@ -3,3 +3,21 @@
 Opens a shell as a different user without needing to authenticate as that user.
 This is similar to the behavior of `su` but it allows to execute privileged
 and/or commands as any other user without needing their password.
+It doesn't use PAM, instead relies on shadow files and the passwd database
+to check if the given password is correct. Support for different methods of
+authentication is planned.
+
+## Installing
+
+To install use `make install` and to uninstall use `make uninstall`, all 
+other documentation is provided as man pages, `man us` will give general
+information about the utility and how to use it and `man us.conf` contains
+info about the config file format.
+
+## Supported platforms
+
+All platforms that store the encrypted password in `/etc/passwd` should be
+supported, which to this day are none. Linux is supported through `shadow(3)`
+and OpenBSD through its API. Support for more systems is planned.
+This program is libc-agnostic as (apart from authentication) it is POSIX
+compliant code.