Include transaction functions in readme
Include transaction functions in readme

Also split 'Usage examples' seconds in 4 parts:
 * Driver creation
 * Session API
 * Transaction functions API
 * Explicit transactions API

neo4j/neo4j-javascript-driver,neo4j/neo4j-javascript-driver,neo4j/neo4j-javascript-driver,neo4j/neo4j-javascript-driver,neo4j/neo4j-javascript-driver