Confusing section links

It was pointed out to me that the links in the introduction next to the tree of STSs are somewhat confusing, specifically these ones: https://github.com/IntersectMBO/formal-ledger-specifications/blob/master/src/Ledger/Introduction.lagda#L176

Every item links to both internal sections and the source code, which is useful, but this isn't super clear from the document itself. I think it would be better to have something such as: 'CHAIN (Section XX, source) is the top level transition ...'.