Update Ozone documentation for Linux Desktop

docs/ozone_overview.md

 # Ozone Overview
 
 Ozone is a platform abstraction layer beneath the Aura window system that is
 used for low level input and graphics. Once complete, the abstraction will
 support underlying systems ranging from embedded SoC targets to new
 X11-alternative window systems on Linux such as Wayland or Mir to bring up Aura
 Chromium by providing an implementation of the platform interface.
 
 ## Guiding Principles
 
@@ skipping 136 matching lines @@
 
 Then to run for example the headless platform:
 
 ``` shell
 ./out/OzoneEmbedded/content_shell --ozone-platform=headless \
                                   --ozone-dump-file=/tmp/
 ```
 
 ### Linux Desktop - ([waterfall](https://build.chromium.org/p/chromium.fyi/builders/Ozone%20Linux/))
 
-**Warning: Experimental support for Linux Desktop is available since m57
-but this is still [in development](https://crbug.com/295089) and currently has
-many bugs.**
+**Warning: Experimental support for Linux Desktop is available since m57 but
+  upstream support has always been a bit fragile. For now, development
+  continues on the
+  [ozone-wayland-dev](https://github.com/Igalia/chromium/tree/ozone-wayland-dev)
+  branch.**
 
 To build `chrome`, do this from the `src` directory:
 
 ``` shell
 gn args out/OzoneLinuxDesktop --args="use_ozone=true enable_package_mash_services=true"
 ninja -C out/OzoneLinuxDesktop chrome
 ```
 Then to run for example the X11 platform:
 
 ``` shell
-./out/OzoneLinuxDesktop/chrome --ozone-platform=x11 \
-                               --mash \
-                               --window-manager=simple_wm
+./out/OzoneLinuxDesktop/chrome --ozone-platform=x11 --mus
 ```
 
 ### GN Configuration notes
 
 You can turn properly implemented ozone platforms on and off by setting the
 corresponding flags in your GN configuration. For example
 `ozone_platform_headless=false ozone_platform_gbm=false` will turn off the
 headless and DRM/GBM platforms.
 This will result in a smaller binary and faster builds. To turn ALL platforms
 off by default, set `ozone_auto_platforms=false`.
@@ skipping 55 matching lines @@
 
 This platform provides support for the [X window system](https://www.x.org/).
 
 ### Wayland
 
 This platform provides support for the
 [Wayland](http://wayland.freedesktop.org/) display protocol. It was
 initially developed by Intel as
 [a fork of chromium](https://github.com/01org/ozone-wayland)
 and then partially upstreamed.
-It is still actively being developed in the chromium tree, feel free to discuss
+It is still actively being developed on the
+[ozone-wayland-dev](https://github.com/Igalia/chromium/tree/ozone-wayland-dev)
+branch, feel free to discuss
 with us on freenode.net, `#ozone-wayland` channel or on `ozone-dev`.
 
 Below are some quick build & run instructions. It is assumed that you are
 launching `chrome` from a Wayland environment such as `weston`. Execute the
 following commands:
 
 ``` shell
 gn args out/OzoneWayland --args="use_ozone=true enable_package_mash_services=true"
 ninja -C out/OzoneWayland chrome
-./out/OzoneWayland/chrome --ozone-platform=wayland \
-                          --mash \
-                          --window-manager=simple_wm
+./out/OzoneWayland/chrome --ozone-platform=wayland --mus
 ```
 
 ### Caca
 
 This platform
 draws graphical output to text using
 [libcaca](http://caca.zoy.org/wiki/libcaca)
 (no GPU support; software
 rendering only). In case you ever wanted to test embedded content shell on
 tty.
@@ skipping 16 matching lines @@
 ./out/OzoneCaca/content_shell
 ```
 
   Note: traditional TTYs are not the ideal browsing experience.<br/>
   ![Picture of a workstation using Ozone/caca to display the Google home page in a text terminal](./images/ozone_caca.jpg)
 
 ## Communication
 
 There is a public mailing list:
 [ozone-dev@chromium.org](https://groups.google.com/a/chromium.org/forum/#!forum/ozone-dev)