Improve documentation for Ozone/Caca

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
 
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 ### 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.
 It has been
 [removed from the tree](https://codereview.chromium.org/2445323002/) and is no
-longer maintained but you can try the
-[latest working revision](https://chromium.googlesource.com/chromium/src/+/0e64be9cf335ee3bea7c989702c5a9a0934af037/ui/ozone/platform/caca/).
-You need additional dependencies (libcaca shared library and development files)
-that are not provided in the sysroot. Here are quick instructions to build and
-run it:
+longer maintained but you can
+[build it as an out-of-tree port](https://github.com/fred-wang/ozone-caca).
+
+Alternatively, you can try the latest revision known to work. First, install
+libcaca shared library and development files. Next, move to the git revision
+`0e64be9cf335ee3bea7c989702c5a9a0934af037`
+(you will probably need to synchronize the build dependencies with
+`gclient sync --with_branch_heads`). Finally, build and run the caca platform
+with the following commands:
 
 ``` shell
-# Do this at revision 0e64be9cf335ee3bea7c989702c5a9a0934af037
-gclient sync --with_branch_heads
 gn args out/OzoneCaca \
         --args="use_ozone=true ozone_platform_caca=true use_sysroot=false ozone_auto_platforms=false toolkit_views=false"
 ninja -C out/OzoneCaca content_shell
 ./out/OzoneCaca/content_shell --disable-setuid-sandbox
 ```
 
   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](https://www.chromium.org/_/rsrc/1396307876689/developers/design-documents/ozone/IMG_20140331_151619.jpg?height=240&amp;width=320)](https://www.chromium.org/developers/design-documents/ozone/IMG_20140331_151619.jpg?attredirects=0)
 
 ## Communication
 
 There is a public mailing list:
 [ozone-dev@chromium.org](https://groups.google.com/a/chromium.org/forum/#!forum/ozone-dev)