Content proposal - Update Brazilian Portuguese documentation for web stories

## 📖 Missing or Out-of-Date Documentation

### Problem
The Web Story Documentation in Portuguese is translated to "História Visual", I believe this is a branding name should stay in English "Criando sua primeira Web Story" instead "Criar uma história visual com AMP" and also the first page has a warning at the bottom "this is a experimental component". I think this is out dated as well

### Location
Documentation > Guides & tutorials > [create your first web story](https://amp.dev/pt_br/documentation/guides-and-tutorials/start/visual_story/?format=stories)

### Content type
Heading session, links, bread crumbs.

### Information architecture (optional)
If you agree with the change I can create a PR to replace the translation for links and headings.

cc.
@morsssss @CrystalOnScript