Update README with useful links and reference docs (#741)
Update README with useful links and reference docs (#741)

Adds reference document links for AWS service guides, SDK getting
started guides, and SDK API references.

Fix #262
Fix #474
zmarois/aws-sdk-go,jasdel/aws-sdk-go,myshen/aws-sdk-go,radeksimko/aws-sdk-go,xibz/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,agworld/aws-sdk-go,zmarois/aws-sdk-go,xibz/aws-sdk-go,radeksimko/aws-sdk-go,calgaryscientific/aws-sdk-go,calgaryscientific/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,myshen/aws-sdk-go,zmarois/aws-sdk-go,yxd-hde/aws-sdk-go,zmarois/aws-sdk-go,aws/aws-sdk-go,yxd-hde/aws-sdk-go,xibz/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,xibz/aws-sdk-go,myshen/aws-sdk-go,agworld/aws-sdk-go,myshen/aws-sdk-go