instructions for manual phantomjs if necessary
instructions for manual phantomjs if necessary

As reported in #675, manual install of phantomjs may be necessary in
caseswhere it is not installed properly by the repository-wide npm
install process. Add instructions to README for cases where this
happens.

supriyantomaftuh/marklogic-samplestack,omkarudipi/marklogic-samplestack,dmcassel/marklogic-samplestack,omkarudipi/marklogic-samplestack,omkarudipi/marklogic-samplestack,supriyantomaftuh/marklogic-samplestack,dmcassel/marklogic-samplestack,marklogic/marklogic-samplestack,supriyantomaftuh/marklogic-samplestack,supriyantomaftuh/marklogic-samplestack,marklogic/marklogic-samplestack,marklogic/marklogic-samplestack,omkarudipi/marklogic-samplestack,dmcassel/marklogic-samplestack,marklogic/marklogic-samplestack,dmcassel/marklogic-samplestack