[doc] Fix broken link in DockerHub

While not ideal, absolute URLs are used as it is the simplest way to
make the links work on GitHub and Docker Hub. These links in cloned
repositories will point back to the main repository and if it is an
issue, the links in the cloned repository need to be updated.

Fixes #408.

Change-Id: I6d9e4bf258325afaefa6c600daf973d0dcf5a94d

README.md

@@ -1,4 +1,14 @@
-![Shaka Packager](docs/shaka-packager.png)
+<!--
+  While not ideal, absolute URLs are used here as it is the simplest way to make
+  the links work on GitHub and Docker Hub. These links in cloned repositories
+  will point back to the main repository and if it is an issue, we suggest
+  updating the links in the cloned repository.
+
+  See https://github.com/google/shaka-packager/issues/408 for the full
+  background.
+-->
+
+![Shaka Packager](https://raw.githubusercontent.com/google/shaka-packager/master/docs/shaka-packager.png)
 
 [![Build Status](https://travis-ci.org/google/shaka-packager.svg?branch=master)](https://travis-ci.org/google/shaka-packager)
 [![Build status](https://ci.appveyor.com/api/projects/status/3t8iu603rp25sa74?svg=true)](https://ci.appveyor.com/project/shaka/shaka-packager)
@@ -56,10 +66,12 @@ Shaka Packager supports:
 There are several ways you can get Shaka Packager.
 
 - Using [Docker](https://www.docker.com/whatisdocker).
-  Instructions are available [here](docs/source/docker_instructions.md).
+  Instructions are available
+  [here](https://github.com/google/shaka-packager/blob/master/docs/source/docker_instructions.md).
 - Get prebuilt binaries from
   [release](https://github.com/google/shaka-packager/releases).
-- Built from source, see [Build Instructions](docs/source/build_instructions.md)
+- Built from source, see
+  [Build Instructions](https://github.com/google/shaka-packager/blob/master/docs/source/build_instructions.md)
   for details.
 
 # Useful Links