docs: update README for pixi-based build workflow (#180)

Replace the miniforge + conda constructor bootstrap with `pixi run
build-installer`, list all four published installers, clarify that the
`version` field in construct.yaml is rolling bookkeeping rewritten at
release time, and fix stale `master` references plus a few typos.

Merge pull request #171 from fstagni/pin_setuptools

fix: pin setuptools to <82.0

Merge pull request #168 from chaen/signularity

chore: add signurlarity

Merge pull request #156 from DIRACGrid/dependabot/github_actions/acti…

…ons/setup-python-6

Bump actions/setup-python from 4 to 6

Merge pull request #151 from chaen/reverse_curl

Reverse curl pin

Merge pull request #150 from chaen/curl

Pin curl until curl/curl#19408 is released

Merge pull request #147 from DIRACGrid/add-py-spy

Add py-spy

Bump version to 2.54a1

Remove ppc64le for now

Revert "HACK: Remove setrlimit in XRootD" (#145)

* Revert "HACK: Remove setrlimit in XRootD"

* Use XRootD >=5.8.0