This extension can be installed via extensions viewlet of VS Code or 'Extensions: install extension' command from the command palette. The author notices that it is developed and tested in SWI-Prolog 7.4.2, ECLiPSe 6.1 and VS Code 1.15 on Debian 9.0 (stretch). It's tested under Windows 10 but not other environments.
Please update to 7.5.13 of swipl if you want to use 'Show all references' feature.
For Windows users: Run VS Code as administrator if going to switch to ECLiPSe from default SWI-Prolog or back to SWI from ECLiPSe. Non-administrator is ok while remain using the same dialect as last time.