Added Easy Install Method (PolymerLabs#3387)

* automated setup process
- converted fresh install instructions into bash script
- tested on Linux

* renamed to setup.sh

* updated setup
- changed shebang
- moved to tools

* updated setup
- fixed paths for tools dir
- tested on linux machine; works fine

* Updated readme with new install mechanism

* echo-ing to indicate progress

* added tracing for failures

* got tracing + early exiting working

* added whitespace for better tracing

* try all sourcing strategies...

* better cmd to get latest npm version

* no hardcoded node version

* cleaned up setup
- rm last step (will print options for user later)
- fixed issue: didn't install nvmrc before using it's value
- formatting

* added coloring + next steps

* better whitespace

* preferring npm ci instead of install
- should be faster than npm install

* better verbage

* stated target OS

.nvmrc

@@ -0,0 +1 @@
+v10.16.0

README.md

@@ -35,6 +35,17 @@ but if for example you see test errors on a version that's a full release later
 patches that will allow more recent versions to operate, ideally without
 requiring an upgrade to our current version.
 
+### Installing the easy way
+
+1) Run the setup script (MacOS, Linux)
+
+   ```
+   $ ./tools/setup
+   ```
+
+2) That's it! (You can skip the next two sections.)
+
+
 ### Installing from scratch
 
 1) Install nvm.

tools/setup

@@ -0,0 +1,50 @@
+#!/bin/sh
+
+ROOT=$(dirname $0)/..
+
+NVM_VERSION="v0.34.0"
+
+YLW="\033[33m"
+RED="\033[91m"
+GRN="\033[92m"
+MAG="\033[95m"
+BLD="\033[1m"
+END="\033[0m"
+
+CMD="$BLD$YLW"
+
+
+fail() {
+    echo "$RED$BLD$1$END"
+    exit 1
+}
+
+status() {
+    echo "$MAG$1$END"
+}
+
+status "1. Install nvm"
+curl -o- "https://raw.githubusercontent.com/creationix/nvm/$NVM_VERSION/install.sh" | sh || \
+    fail "Failed to download nvm version $NVM_VERSION." 
+
+status "1.1 ensure nvm is in your current process"
+. ~/.nvm/nvm.sh || source ~/.nvm/nvm.sh
+
+status "2. Install node"
+(cd $ROOT && nvm install && nvm use) || fail 'Failed to install target node version.' 
+
+status "3. Update npm to latest version"
+nvm install-latest-npm  || fail 'Failed to update npm to latest version.'
+
+status "4. Install dependencies"
+(cd $ROOT && npm ci) || fail 'Failed to install dependencies.' 
+
+
+echo "$GRN$BLD\n\nSETUP COMPLETE\n$END"
+echo "Next, try the following:\n"
+echo "- Setup git hooks: $CMD\`git config core.hooksPath tools/hooks\`$END"
+echo "- Serve the project: $CMD\`npm start\`$END"
+echo "- Run tests:"
+echo "  - $CMD\`./tools/sigh test\`$END"
+echo "  - $CMD\`./tools/test\`$END"
+