[SCB-29] add README document for config-apollo

[lijasonvip]

Signed-off-by: lijasonvip libo75@huawei.com

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[coveralls]

Coverage decreased (-0.02%) to 87.166% when pulling 8d7ccee on lijasonvip:config-doc into e1137b4 on apache:master.

[liubao68]

The referenced manual still use io.servicecomb package， please changed it