Readme: mention to install autoconf (#984)
Readme: mention to install autoconf (#984)

* Readme: mention to install autoconf

Autoconf needs to be installed at least when building on raspian.

Observed issue without autoconf installed:

error when running npm start

Module build failed: Error: spawn /home/pi/things/gateway/node_modules/gifsicle/vendor/gifsicle ENOENT

Might only be required for ARM GNU/Linux

* Update README.md

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