message: Build documentation update (ubuntu_1804)
diff: # Building and running the MLDB Community Edition Docker image
  -These instructions are designed for a vanilla installation of **Ubuntu 14.04** and its default compiler, **GCC 4.8** and assume that you have a Github account with [SSH keys](https://help.github.com/categories/ssh/).
  +These instructions are designed for a vanilla installation of **Ubuntu 16.04 or 18.04** and the **GCC 6, 7 or 8** compiler and assume that you have a Github account with [SSH keys](https://help.github.com/categories/ssh/).
  -It will take around **45 minutes on a 32-core machine with 244GB of RAM** to run through these steps (i.e. on an Amazon EC2 r3.8xlarge instance) and longer on smaller machines. However, you can get up and running in 5 minutes by [using a pre-built Docker images of the MLDB Enterprise Edition](http://mldb.ai/doc/#builtin/Running.md.html) for free with a trial license, which can be obtained instantly by filling out [this form](http://mldb.ai/licensing.html).
  +It will take around **5 minutes on a 32-core machine with 244GB of RAM** to run through these steps (i.e. on an Amazon EC2 r3.8xlarge instance) and longer on smaller machines.
  +
  +## Installing the correct compiler toolchain
  +
  +MLDB requires GCC version 6 or above, or clang 3.8 or above. If you are
  +using clang, then g++ must also be installed as on Ubuntu, clang is
  +configured to use the c++ header files and standard library from GCC.
  +
  +### Under Ubuntu 18.04
  +
  +```bash
  +apt-get install -y g++ # To compile with GCC 7 (default)
  +```
  +
  +If you want to use a different toolchain (if you're not sure, you don't),
  +you will need to install it:
  +
  +```bash
  +apt-get install -y g++-6 # To compile with GCC 6 using toolchain=gcc6
  +apt-get install -y g++-8 # To compile with GCC 8 using toolchain=gcc8
  +apt-get install -y clang-6.0 g++ # To compile with clang version 6 using toolchain=clang
  +```
  +
  +### Under Ubuntu 16.04
  +
  +Since g++ 6.0 or later is not available on Ubuntu 16.04 as a native package, it
  +needs to be added as an apt source. If you attempt to build MLDB without
  +installing a newer gcc, you will get a message that gcc 5 (which comes with
  +Ubuntu 16.04) is not supported.
  +
  +```bash
  +add-apt-repository ppa:ubuntu-toolchain-r/test
  +apt update
  +```
  +
  +and then one of
  +
  +```bash
  +apt-get install -y g++-8 # To compile with GCC8 using toolchain=gcc8 (recommended)
  +apt-get install -y g++-6 # To compile with GCC6 using toolchain=gcc6
  +apt-get install -y g++-7 # To compile with GCC7 using toolchain=gcc7
  +apt-get install -y g++-8 clang-6.0 # To compile with clang 6.0 using toolchain=clang
  +```
  +
  +You will need to set the `toolchain=gcc6`, `toolchain=gcc7`, `tool
  ## Installing system dependencies via `apt-get`
  @@ -66,9 +110,9 @@ git clone git@github.com:mldbai/mldb.git
  cd mldb
  git checkout release_latest
  git submodule update --init --recursive
  -make dependencies
  -make -k compile
  -make -k test
  +make dependencies toolchain=<see above>
  +make -k compile toolchain=<see above>
  +make -k test toolchain=<see above>
  ```
  To speed things up, consider using the `-j` option in `make` to leverage
  