man: add weston-drm page

Add some documentation about the DRM backend into its own man page, and
refer to it in weston(1).

Environment variable, that are reserved for backends, and currently used
only by the DRM backend, are moved to weston-drm page.

NOTE: This is a candidate for the stable branch
Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/man/weston.man b/man/weston.man
index efb6d2b..1bf87d8 100644
--- a/man/weston.man
+++ b/man/weston.man
@@ -30,7 +30,9 @@
 .TP
 .I drm-backend.so
 The DRM backend uses Linux KMS for output and evdev devices for input.
-It supports multiple monitors in a unified desktop with DPMS.
+It supports multiple monitors in a unified desktop with DPMS. See
+.BR weston-drm (7),
+if installed.
 .TP
 .I wayland-backend.so
 The Wayland backend runs on another Wayland server, a different Weston
@@ -132,14 +134,8 @@
 with this value in the environment for all child processes to allow them to
 connect to the right server automatically.
 .SS DRM backend options:
-.TP
-\fB\-\-connector\fR=\fIconnectorid\fR
-.TP
-.B \-\-current\-mode
-.TP
-\fB\-\-seat\fR=\fIseatid\fR
-.TP
-\fB\-\-tty\fR=\fItty\fR
+See
+.BR weston-drm (7).
 .
 .SS Wayland backend options:
 .TP
@@ -203,10 +199,6 @@
 .TP
 .B WAYLAND_SOCKET
 .TP
-.B WESTON_TTY_FD
-.TP
-.B WESTON_LAUNCHER_SOCK
-.TP
 .B XCURSOR_PATH
 Set the list of paths to look for cursors in. It changes both
 libwayland-cursor and libXcursor, so it affects both Wayland and X11 based
@@ -251,6 +243,7 @@
 weston
 .
 .\" ***************************************************************
-.\".SH "SEE ALSO"
+.SH "SEE ALSO"
+.BR weston-drm (7)
 .\".BR weston-launch (1),
 .\".BR weston.ini (5)