Add & modify REST API reference page messages

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/resources/messages.properties

@@ -55,7 +55,15 @@ page.text.list.json          = Get
 
 page.text.apiref.endpoints   = REST API end points
 page.text.apiref.examples    = Direct search examples
-page.text.apiref.add         = Adding books (Unix-alike clients)
+page.text.apiref.add         = Adding a book (Unix-alike clients)
+page.text.apiref.edit        = Editing an existing book (Unix-alike clients)
+page.text.apiref.delete      = Deleting an existing book (Unix-alike clients)
+page.text.apiref.get         = Getting information about an existing book (Unix-alike clients)
+
+page.text.apiref.edit.info   = Where suffix number 2 is a book ID
+
+page.text.apiref.links.title = Direct link
+page.text.apiref.link        = Link
 
 page.text.error              = Error while processing your request