chore(readme): add doc about optional dependencies
chore(readme): add doc about optional dependencies

dlabrecq/patternfly-ng,dlabrecq/patternfly-ng,patternfly/patternfly-ng,patternfly/patternfly-ng,patternfly/patternfly-ng,patternfly/patternfly-ng,dlabrecq/patternfly-ng,dlabrecq/patternfly-ng