Update dependencies and metadata in pyproject.toml

Lower setuptools version requirement for compatibility reasons.
Refine description for clarity and switch to the 'license' key with a comment explaining future plans.

pyproject.toml

 [build-system]
-requires = ["setuptools>=77.0", "wheel", "cmake>=3.21"]
+requires = ["setuptools>=75.0", "wheel", "cmake>=3.21"]
 build-backend = "setuptools.build_meta"
 
 [project]
@@ -9,10 +9,10 @@ authors = [
     { name = "Gregoire Malandain", email = "gregoire.malandain@inria.fr" },
     { name = "Jonathan Legrand", email = "jonathan.legrand@ens-lyon.fr" }
 ]
-description = "Python wrappers for the vt library"
+description = "Python wrappers for the 'vt' image processing library."
 readme = "README.md"
 requires-python = ">=3.8"
-license-files = ["LICENSE.txt"]
+license = { 'file' = "LICENSE.txt" }  # update to use 'license-files' when "setuptools>=77.0" is on anaconda.org
 classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Intended Audience :: Science/Research",