[jqassistant-archive/jqa-manual#7] Assigned an id to the toplevel hea…

…dline, so what it can be easily referened from the jQAssistant reference

pom.xml

@@ -64,6 +64,7 @@
  <org.springframework.version>3.0.0.RELEASE</org.springframework.version>
  <org.springframework.boot_version>1.3.3.RELEASE</org.springframework.boot_version>
  <org.springframework.data_version>1.9.4.RELEASE</org.springframework.data_version>
+ <asciidoctor.toplevelid>spring-plugin</asciidoctor.toplevelid>
  </properties>
 
  <build>