JCR-227: Point to "Building Jackrabbit" instead of "README.txt" in "First Steps". Also added a brief intro and changed the section levels for clarity.
JCR-227: Point to "Building Jackrabbit" instead of "README.txt" in "First Steps". Also added a brief intro and changed the section levels for clarity.

git-svn-id: e3d4743c6b03e3f6fd6d8117e7616b4c02d9b980@354359 13f79535-47bb-0310-9956-ffa450edef68

apache/jackrabbit,apache/jackrabbit,apache/jackrabbit