[tasklist] doc: add manual for content -> multi languages

[xiaohanyu]

Description

Add a section with path: content -> multi languages.

The section will decribe PPResume native support for multi languages resumes.

Todo list

### Tasks
- [ ] https://github.com/ppresume/community/issues/111
- [ ] https://github.com/ppresume/community/issues/112
- [ ] https://github.com/ppresume/community/issues/113
- [ ] https://github.com/ppresume/community/issues/114
- [ ] https://github.com/ppresume/community/issues/115
- [ ] https://github.com/ppresume/community/issues/116

[xiaohanyu]

The landing page for content -> multi languages: