Added instructions describing how to build LibVLC in a docker container

Current instructions for building LibVLC were not clear and mentioned docker container failed to build.

Updated instructions using UWP docker image from CI that should work all the time.

README.md

@@ -61,8 +61,8 @@ winpty docker run -it --rm --net=host -v /${PWD}:/vlc registry.videolan.org/vlc-
 ```
 - In your docker container clone repo as described above. If you clone on host Windows machine,
 you'll likely have CRLF line endings messed up.
-- cd to ```vlc-winrt/libvlc``` and run ``` ./compile.sh x86_64 win10``` or using different architecture.
-- Compiled libraries will be dropped under one of vlc-winrt/libvlc/vlc/winrt-... folders depending on the architecture.
+- cd to `/vlc/vlc-winrt/libvlc` and run `./compile.sh x86_64 win10` or using different architecture.
+- Compiled libraries will be dropped under one of `vlc-winrt/libvlc/vlc/winrt-...` folders depending on the architecture.
 
 ## Contribute