Add Spring Boot Hello World guide

Add Spring Boot Hello World Guide

Fixes gh-3866

docs/docs.gradle

@@ -18,6 +18,8 @@ project('manual') {
 
 	asciidoctor {
 		backends = ['docbook5']
+		def ghTag = snapshotBuild ? 'master' : project.version
+		def ghUrl = "https://github.com/spring-projects/spring-security/tree/$ghTag"
 		options = [
 		  eruby: 'erubis',
 		  attributes: [
@@ -33,6 +35,8 @@ project('manual') {
 			  'spring-security-version' : project.version,
 			  'spring-version' : springVersion,
 			  revnumber : project.version,
+			  'gh-url': ghUrl,
+			  'gh-samples-url': "$ghUrl/samples",
 			  docinfo : ""
 		  ]
 		]