Docs build: vectorise example 8 referenced but does not exist

[theoturner]

In the docs build, the source for vectorise references example 8 which does not exist (yet).

A quick fix would be to remove lines 280-282 in [path]/ledger/docs/source/vectorise/index.rst until example 8 is added.

Error: [path]/ledger/docs/source/vectorise/index.rst:280: WARNING: Include file '[path]/ledger/libs/vectorise/examples/08_dot_product/main.cpp' not found or reading it failed