Write docs for `vike-vue-pinia` and `vike-vue-query`

[brillout]

New docs for vike-vue live at vike.dev, for example:

• https://vike.dev/clientOnly#vue
• https://vike.dev/bodyHtmlEnd
• https://vike.dev/onBeforeRenderClient

But for vike-vue-pinia and vike-vue-query I think it's better we write the docs in the README.md file.

So far vike-vue-pinia and vike-vue-query don't have any documentation, contribution welcome to create some.