docs: correct stale directory paths in the php and website READMEs

[prql-bot]

Two READMEs point at directories that no longer exist, so following either one fails immediately. Both are leftovers from moves that didn't update the surrounding prose.

• prqlc/bindings/php/README.md said to spawn the nix shell from prql-php/; the binding lives at prqlc/bindings/php/.
• web/website/README.md said to serve with cd website && hugo server. There's no website/ at the repo root — it's web/website/ — and the repo already has a task for this, so the README now points at task web:run-website rather than a path that can go stale again.

No changelog entry, matching #6234 and other docs-only fixes. No test either — these are prose corrections; the verification is that the paths they now name exist and the task resolves.

Verification

Current state at e0540ff:

$ ls -d prql-php
ls: cannot access 'prql-php': No such file or directory
$ ls -d website
ls: cannot access 'website': No such file or directory

task web:run-website resolves through the root Taskfile.yaml's web: include (taskfile: ./web, dir: ./web) to web/Taskfile.yaml, whose run-website task sets dir: website and runs hugo server --bind 0.0.0.0 — the same command the README described, from the directory that actually holds config.yaml.

prettier --check passes on both files.