doc : add event type `ping`

[javathought]

Version

• vert.x core: 3.5.3
• vert.x tcp eventbus bridge: 3.5.3

Context

On documentation (example on https://vertx.io/docs/vertx-tcp-eventbus-bridge/java/) : The ping event type is not present in the doc :

• ping is not documented (and thus pong is not present in the list of types sent back to the client)

[javathought]

Updated as part was a duplicate of #34 .

[javathought]

ping issue is closed (#37 )

[javathought]

remaining : complete the doc

[gaol]

I think this can be closed because both ping and pong are in doc now. :)