Ignore the files/templates folder

[pepelsbey]

We’re planning to start using the files/templates folder as a folder with inert template files. And we want rari to ignore it. Now it throws errors:

The document's slug (MDN/Writing_guidelines/Page_structures/Page_types/WebExtension_API_event_page_template) doesn't match its disk folder name (en-us/mdn/writing_guidelines/page_structures/page_types/webextension_api_event): expected path (en-us/mdn/writing_guidelines/page_structures/page_types/webextension_api_event_page_template)

Folder structure example

files/templates/
└── webextensions
    ├── api-event.md
    ├── api-function.md
    ├── api-overview.md
    ├── api-property.md
    ├── api-type.md
    └── manifest-key.md

We might also start using it for the Firefox release notes template, etc.

• See the PR adding such files