Add instructions to install RVM in MacOS

From High Sierra to Mojave

Author: cesc1989

macos/install_rvm.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+brew install gpg
+
+gpg --keyserver hkp://pool.sks-keyservers.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
+\curl -sSL https://get.rvm.io | bash -s stable
+
+echo "Sourcing RVM and reloading shell"
+. /Users/$(whoami)/.rvm/scripts/rvm
+
+echo "RVM requirements"
+rvm requirements
+
+echo "Installing ruby-2.5.3"
+rvm install ruby-2.5.3
+
+echo "Setting ruby-2.5.3 as default"
+rvm --default use ruby-2.5.3
+
+echo "Install bundler"
+gem install bundler --no-document
+
+# This wouldn't work because it is executed in a different
+# shell which gets invoked inside the script and not the
+# terminal window
+echo "...again"
+. /Users/$(whoami)/.rvm/scripts/rvm