Update README.md

Added comment on running it without a server
working towards #199
Merge commit '9a2d1cbf1bafe8c54dd15ffe96df22ef455c58b1' into SetSelectionRefactor
wip on adding additional attributes about datasets
look and feel adapted for #199
fixes #202
working towards dataset information #144
Merge branch 'master' of https://github.com/VCG/UpSet
fine-tuned label names for set selection; title cased stuff for #199
implementing dataset information, fixing #144. Providing metadata for multiple datasets
Merge branch 'master' into gh-pages