examples should indicate which params are new/optional

[jbandhauer]

Some optional params have been added since Looker first added SSO signing support. Not all params are supported in older Looker versions. This is especially important for those params that are used in building the signature because older Looker versions will fail to validate signatures that incorporate params that those versions don't recognize. This can be very frustrating to figure out. More info in the examples would help consumers of these examples who might be working with slightly older Lookers.