Update README with building section

src/main/asciidoc/README.adoc

@@ -5,3 +5,7 @@ include::intro.adoc[]
 == Quick Start
 
 include::quickstart.adoc[]
+
+== Building
+
+include::https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/src/main/asciidoc/building.adoc[]

src/main/ruby/generate_readme.sh

@@ -18,7 +18,7 @@ file = ARGV[0] if ARGV.length>0
 
 srcDir = File.dirname(file)
 out = "// Do not edit this file (e.g. go instead to src/main/asciidoc)\n\n"
-doc = Asciidoctor.load_file file, safe: :safe, parse: false
+doc = Asciidoctor.load_file file, safe: :safe, parse: false, attributes: 'allow-uri-read'
 out << doc.reader.read
 
 unless options[:to_file]