Update BUILDING.md

BUILDING.md

@@ -54,11 +54,14 @@ Development
 -----------
 
 1. Install dependencies `apt-get install git cmake build-essential g++ libglew-dev libfreeimage-dev libtbb-dev libsndfile1-dev libopenal-dev libjpeg-dev libfreetype6-dev libglfw3-dev libxcursor-dev libxinerama-dev libxi-dev libsfml-dev libvpx-dev libwebp-dev liblzma-dev libfdk-aac-dev libmp3lame-dev libopus-dev libtheora-dev libx264-dev libx265-dev libbz2-dev libssl-dev libcrypto++-dev librtmp-dev libgmp-dev libxcb-shm0-dev libass-dev libgconf2-dev`
-2. `git clone --single-branch --branch master https://github.com/CasparCG/server casparcg-server-master`
-3. `cd casparcg-server-master`
-4. Extract Boost, FFmpeg and CEF from the docker images via `sudo ./tools/linux/extract-deps-from-docker`. Alternatively these can be prepared manually by following the steps laid out in each Dockerfile
-5. `mkdir build && cd build`
-6. `cmake ../src`
-7. `make -j8`
+2. Install Docker by following installation instructions from [Docker Docs][1]
+3. `git clone --single-branch --branch master https://github.com/CasparCG/server casparcg-server-master`
+4. `cd casparcg-server-master`
+5. Extract Boost, FFmpeg and CEF from the docker images via `sudo ./tools/linux/extract-deps-from-docker`. Alternatively these can be prepared manually by following the steps laid out in each Dockerfile
+6. `mkdir build && cd build`
+7. `cmake ../src`
+8. `make -j8`
 
 If all goes to plan, a folder called 'staging' has been created with everything you need to run CasparCG server.
+
+[1]: https://docs.docker.com/install/linux/docker-ce/ubuntu/