Add Privacy Principles (#1789)

Close #1788, adding the suggested spec to the list.

### Changes to `index.json`
This update would trigger the following changes in `index.json`:

<details><summary>Add spec (1)</summary>

```json
{
  "url": "https://www.w3.org/TR/privacy-principles/",
  "seriesComposition": "full",
  "shortname": "privacy-principles",
  "series": {
    "shortname": "privacy-principles",
    "currentSpecification": "privacy-principles",
    "title": "Privacy Principles",
    "shortTitle": "Privacy Principles",
    "releaseUrl": "https://www.w3.org/TR/privacy-principles/",
    "nightlyUrl": "https://w3ctag.github.io/privacy-principles/"
  },
  "organization": "W3C",
  "groups": [
    {
      "name": "Technical Architecture Group",
      "url": "https://www.w3.org/2001/tag/"
    }
  ],
  "release": {
    "url": "https://www.w3.org/TR/privacy-principles/",
    "status": "Note",
    "filename": "Overview.html"
  },
  "nightly": {
    "url": "https://w3ctag.github.io/privacy-principles/",
    "status": "Editor's Draft",
    "alternateUrls": [],
    "repository": "https://github.com/w3ctag/privacy-principles",
    "sourcePath": "index.html",
    "filename": "index.html"
  },
  "title": "Privacy Principles",
  "source": "w3c",
  "shortTitle": "Privacy Principles",
  "categories": [],
  "standing": "good"
}
```
</details>

### Tests
These changes look good! 😎

Co-authored-by: browser-specs-bot <>

Author: browser-specs-bot

Diff for: specs.json

@@ -1513,6 +1513,7 @@
   "https://www.w3.org/TR/pointerevents4/",
   "https://www.w3.org/TR/pointerlock-2/",
   "https://www.w3.org/TR/presentation-api/",
+  "https://www.w3.org/TR/privacy-principles/",
   "https://www.w3.org/TR/proximity/",
   "https://www.w3.org/TR/pub-manifest/",
   "https://www.w3.org/TR/push-api/",