Suggestion: add build instructions for CTL interpreter

[Paul Matthijsse]

Hello, I suggest to add the following build instructions for the CTL interpreter on the “Build ART on Ubuntu” page on Bitbucket.

$ sudo apt install libilmbase-dev libopenexr-dev
$ git clone https://github.com/ampas/CTL.git
$ cd CTL
$ mkdir build && cd build
$ cmake ..
$ make
$ sudo make install

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