Fulfil ASF requirements on the website and the repo

The ASF has [a number of requirements](https://incubator.apache.org) for incubator projects. This is the collection issue for all of the ones relating to the PouchDB website and repo. There is an [additional issue with tasks that need to happen within the ASF infrastructure](https://github.com/apache/pouchdb/issues/9259), such as submitting our logo to them etc.

From the [website](https://incubator.apache.org/guides/sites.html) and [branding](https://incubator.apache.org/guides/branding.html) guides:

- [x] We MUST refer to PouchDB as "Apache PouchDB" from now on.
- [x] We MUST mention that the project is under incubation. Suitable mentions include:
- "Apache PouchDB is currently undergoing Incubation at the Apache Software Foundation."
- Referring to the podling as "Apache PouchDB (Incubating)."

- [x] We MUST include these statements in the README file of each repository belonging to the podling
- [x] We CAN also refer the podling as "Apache PouchDB (Incubating)" in the GitHub repository description.
- [x] We MUST update the website navigation to link to a variety of ASF URLs, as detailed [here](https://www.apache.org/foundation/marks/pmcs#navigation). These will have to go in a dropdown, see how [casbin](https://casbin.apache.org/) does it.
- [x] "Every product homepage and any overview download page for the product MUST include a prominent reference to the product as "Apache PouchDB", and must include a brief, one-sentence description of the purpose and function of the software product itself. For example:

> The Apache Xerces XML parsing library software provides a complete implementation of the XML 1.0 parsing specification, and is easily configurable and compliant with current standards.
- [x] We MUST include [trademark attributions](https://www.apache.org/foundation/marks/pmcs#attributions) on the website, specifically (See also the [casbin](https://casbin.apache.org/) footer for examples of most of these):

- [x] This in the footer:

> Apache PouchDB, PouchDB, Apache, the Apache logo, and the Apache PouchDB project logo are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.
- [x] "Add `™` to the first main occurrence of the "Apache PouchDB" project name, both in header/title text and at the name's first appearance in running text."
- [x] Add generic trademark attribution as well (also in the footer):
> All other marks mentioned may be trademarks or registered trademarks of their respective owners.
- [x] Add a `™` to the PouchDB logo itself

ASF and incubator logos (https://incubator.apache.org/guides/press-kit.html)
- [x] Add a fitting ASF incubator logo to the footer and info -> https://incubator.apache.org/guides/press-kit.html
- [x] Add the [asf logo](https://www.apache.org/foundation/press/kit/poweredBy/Apache_PoweredBy.svg) to the footer

- [x] We SHOULD add a link to the [Disclaimers](https://incubator.apache.org/guides/branding.html#Disclaimers) in the README file, the regular one for ASF releases is the one we want. So this needs to be in the footer of the website (e.g. [casbin](https://casbin.apache.org/)) and exist as a separate [DISCLAIMER file](https://github.com/apache/casbin/blob/master/DISCLAIMER) in the repo.
- [ ] We should also aim to update the "PouchDB is used by"-section with up-to-date users.
- [ ] "Every podling SHOULD maintain an incubation status file under: http://incubator.apache.org/projects/podlingname.html (this is generated)." – I have not found out how this works exactly, so tbd on this.

Review the remaining unchecked items in the issue, especially the website's “PouchDB is used by” section, the incubation status file process, and the README/DISCLAIMER requirements. Start with the linked ASF website, branding, press-kit, and disclaimer guides, then inspect the website and repository documentation. Done means the remaining applicable ASF requirements are completed or clarified.

Written by the indexing model from the issue text.