Update readme with default_text_charset for s3
Update readme with default_text_charset for s3

travis-ci/dpl,Misfit-SW-China/dpl,travis-ci/dpl,mattk42/dpl,travis-ci/dpl,pengsrc/dpl,testfairy/dpl,computology/dpl,testfairy/dpl,testfairy/dpl