Add better installation instructions.

README.md

@@ -15,17 +15,47 @@ The following programs/libraries need to be installed on your system:
 - PNG++
 
 Note that most of these are dependencies of Caffe, and thus will
-probably already be on your system.
+probably already be on your system. For OS-specific instructions, see
+below.
+
+### Arch Linux
+
+1. Install either `caffe` or `caffe-cpu` from the AUR.
+2. Install other dependencies:
+    - `png++`
+    - `cmake`
+    - `freeglut`
+3. Do the build as normal
+
+### Ubuntu
+
+Caffe is available from the Ubuntu repositories from version 17.10
+(Artful Aardvark) onwards, and can be used to simplify the installation
+process. The commands required are as follows:
+
+    # Install dependencies
+    sudo apt install caffe-cpu-dev freeglut3-dev libpng++-dev build-essential cmake
+
+    # Do the build normally
+
+Older versions of Ubuntu need some help, as the `caffe` package does not
+exist, and the supplied `cmake` version is too old.
+
+1. First, install a recent version of [cmake](https://cmake.org/). Any
+   version from 3.8 onwards will do.
+2. Then, install caffe from source. Installation instructions can be
+   found [on the Caffe
+   website](http://caffe.berkeleyvision.org/install_apt.html). Be sure
+   to also install the development headers.
+3. Run the build as normal.
 
 ## Building
 
 The build process is based on CMake. This means you can easily create a
 build as follows. Starting from the project root:
 
-```
-mkdir build && cd build
-cmake ..
-make
-```
+    mkdir build && cd build
+    cmake ..
+    make
 
 Compilation is a little slow due to the inclusion of Boost.