💡 document relationship between webjars, gradle, npm, and vue

[ChristianMurphy]

💡 could you add a note **Note:**, and references on webJars. this can help understanding on what webjars are, and the relationships between gradle - npm - vue. the build process and the development process.
understanding: there are some people who do not speak / understand well English, and they need to have clear explanations. [when - I do hope so - this 🎉 update will be merged, a few days after, it will be in french 🇫🇷 - trust me 😉 ] see the up-to-date Vue.js doc in french

Originally posted by @cousquer in https://github.com/_render_node/MDE3OlB1bGxSZXF1ZXN0UmV2aWV3MjAzNjI2NDMz/pull_request_reviews/more_threads