doc: vlc.1: add VLC_LIB_PATH in manpages

The VLC_LIB_PATH environment variable has been introduced in commit
75308a48f2 to override the path where to
find the executables and other architecture-dependant files.

doc/vlc.1

@@ -89,6 +89,11 @@ used by the OSSv4 output plugin.
 .B VLC_DATA_PATH
 The directory containing VLC run-time data files (e.g. /usr/share/vlc).
 
+.TP
+.B VLC_LIB_PATH
+The directory containing VLC binary folder, which is used for the dynamically
+loaded libraries and architecture-dependant executables (e.g. /usr/lib/).
+
 .TP
 .B VLC_PLUGIN_PATH
 An extra directory to load VLC plugins from.