New documentation for building/running the node

doc/building-running.md

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+**Validated: 2020/03/26**
+
+# Building Cardano Node
+
+There are a number of ways the Cardano Node can be built and run, but the following document
+details the Nix and Ubuntu/Debian methods. The Nix method is probably more robust and foolproof
+than installing on Ubuntu/Debian.
+
+
+### Building under Nix
+
+The [Nix Package Manager][nix] can be installed on most Linux distributions by downloading and
+running the installation script:
+```
+curl https://nixos.org/nix/install > install-nix.sh
+./install-nix.sh
+```
+and following the directions.
+
+To improve build speed, it is possible to set up a binary cache maintained by IOHK (**this is
+optional**):
+```
+sudo mkdir -p /etc/nix
+cat <<EOF | sudo tee /etc/nix/nix.conf
+substituters = https://hydra.iohk.io https://cache.nixos.org/ http://cache.loony-tools.dev.iohkdev.io
+trusted-substituters =
+trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= loony-tools:pr9m4BkM/5/eSTZlkQyRt57Jz7OMBxNSUiMC4FkcNfk=
+EOF
+```
+
+Once Nix is installed, log out and then log back in and then in a `nix-shell` session:
+```
+git clone https://github.com/input-output-hk/cardano-node
+cd cardano-node
+nix-build -A scripts.mainnet.node -o mainnet-node-local
+./mainnet-node-local
+```
+
+### Building Under Debian and Ubuntu
+The instructions for Debian and Ubuntu are largely identical.
+
+Since neither Debian nor Ubuntu are likely to have the required version of GHC and cabal they
+will probably need to be installed manually. The required versions are [GHC 8.6.5][ghc865] and
+[Cabal-3.0][cabal30].
+
+The code in the Haskell node also requires that the development packages for a couple of Linux
+system libraries be installed:
+```
+sudo apt-get update
+sudo apt-get libgmp-dev libssl-dev libtinfo-dev libsystemd-dev zlib1g-dev
+```
+
+Finally the Cardano Node git repo can be cloned and the code built:
+```
+git clone https://github.com/input-output-hk/cardano-node
+cd cardano-node
+cabal build all
+cabal run cardano-node -- -help
+```
+
+
+[cabal30]: https://www.haskell.org/cabal/download.html
+[ghc865]: https://www.haskell.org/ghc/blog/20190423-ghc-8.6.5-released.html
+[nix]: https://nixos.org/nix/