docs: give the install script's address as configfile.sh/install.sh

[mindsers]

Context

configfile 1.1.0 ships standalone binaries with an install script, docs/public/install.sh. The docs site publishes it to GitHub Pages on each release, at https://docs.configfile.sh/install.sh, and the docs give that address:

curl -fsSL https://docs.configfile.sh/install.sh | sh

The project's landing page lives at the shorter configfile.sh, a separate site built from mindsers/configfile-website. mindsers/configfile-website#11 makes configfile.sh/install.sh redirect (302) to the docs address.

What changes

• Address: the README, the installation page and the new-machine guide give https://configfile.sh/install.sh.
• The script: it stays where it is (docs/public/install.sh) and is still published the same way. Its header gives the new address, and says the file must stay in docs/public/, since both addresses rely on it.
• Comments: those in the CI workflow and the installer tests mention the redirect.
• CHANGELOG: an Unreleased entry gives the new address. The address in the 1.1.0 entry keeps working, so released entries are left as they are.

Compatibility

• https://docs.configfile.sh/install.sh keeps working.
• Commands must follow redirects. All documented ones use curl -fsSL, and wget follows redirects by default.