Stop pointing the docs at another fork's site

[Guiw5]

homepage in package.json and every demo link in the README pointed at
react-spring-bottom-sheet.nipesolutions.com. That domain does not serve this fork: it
belongs to NIPE-Solutions/react-spring-bottom-sheet, a different fork of the same
original, with its own rewritten docs.

Measured on the live HTML: zero occurrences of Guiw5, of guiw5-bottom-sheet, or of
any heading from this repo's fixtures, against 24 occurrences of
react-spring-bottom-sheet and links to both stipsan's and NIPE-Solutions' repos.

The practical effect was that npm's package page sent people to another project's
website, and the six demo links all 404'd, because that site has no /fixtures/*
routes. This repo's own build produces them fine.

Changes

• homepage now points at this repository, which is what npm links to.
• The logo at the top of the README was an image hotlinked from that domain, with no
  local copy in public/. Removed rather than left embedding another project's asset.
• The five demo headings are plain text now. The View demo code link under each one
  already points into this repo, so nothing is lost.
• The Demos heading explains how to run them locally, including the network URL Next
  prints, which is how you open a fixture on a phone.

Hosting this fork's docs and pointing everything back at a real URL is the better fix,
but it needs a Vercel project on the owner's account. This removes the wrong links in
the meantime.

Test plan

• npm test: lint, 32 tests, library build, docs build
• No reference to the domain remains in README.md or package.json