update docs to reference new location of requirements file (refs #197)
update docs to reference new location of requirements file (refs #197)

peterayeni/rapidsms,eHealthAfrica/rapidsms,lsgunth/rapidsms,peterayeni/rapidsms,catalpainternational/rapidsms,catalpainternational/rapidsms,ehealthafrica-ci/rapidsms,lsgunth/rapidsms,caktus/rapidsms,lsgunth/rapidsms,catalpainternational/rapidsms,caktus/rapidsms,eHealthAfrica/rapidsms,ehealthafrica-ci/rapidsms,peterayeni/rapidsms,eHealthAfrica/rapidsms,caktus/rapidsms,lsgunth/rapidsms,ehealthafrica-ci/rapidsms,peterayeni/rapidsms,catalpainternational/rapidsms