README: Add basic build directions In particular, highlight the use of configure flags to control locating X11 keyboard stuff when building for Wayland. Of particular note, if the locale root is not specified, then xkbcommon will look for them under $prefix (i.e. /usr/local/share/X11/locale). But unless the user has specifically installed them there, it is better to look in the standard system location, /usr/share/X11/locale. Otherwise, xkbcommon will error when it can't find them, e.g.: xkbcommon: ERROR: ~/.XCompose:4:9: failed to expand %L to the locale Compose file xkbcommon: ERROR: ~/.XCompose:4:12: unterminated string literal Signed-off-by: Bryce Harrington <bryce@osg.samsung.com> Signed-off-by: Ran Benita <ran234@gmail.com>