[docs]Refine "The Pulsar Java client" content (#5853)
[docs]Refine "The Pulsar Java client" content (#5853)

* Refine "The Pulsar Java client" content

Refine "The Pulsar Java client" content in aspects of grammar, spelling, wording, etc.

* revise the document per Jennifer's comments

* Update client-libraries-java.md

merlimat/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,yahoo/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar