Improve documentation of some vocabulary with examples

[Aklakan]

Although there are labels and comments in the ontology file, especially the selectivity-related metrics are probably not very clear.
In addition, it also makes sense to generate a reference page from a markdown table derived from the ontology file.

• lsqo:in
• lsqo:tpSelJoinVarRestricted
• hypertree model of bgps