[BEAM-1559] Reference HBase support in the documentation

[tom-haines]

References to the HBase IO connector recently added are updated into the documentation.

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Jenkins built the site at commit id 1f44221 with Jekyll and staged it here. Happy reviewing.

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[jbonofre]

R: @jbonofre

[davorbonaci]

LGTM. This is clearly an improvement, so merging. Thanks @tom-haines!

@jbonofre, perhaps you want to submit a separate PR to list other missing ones?