docs(python): make the PyPI description a short readable introduction

changes/unreleased/python-readme-pypi.changed.md

@@ -0,0 +1 @@
+- **The `opensysml` PyPI page reads as a short introduction.** The Python package's README, which PyPI renders as the project description, is the install command, a quickstart, a short account of how the service is found, and links to the guides; the walls of implementation detail that 0.9.1 published move to the [service guide](https://opensysml.org/clients/python/service/) and the API reference.

client/python/README.md

@@ -45,26 +45,33 @@ print(model.eval("mass", subject="Demo::sedan"))
 1800.0
 ```
 
-## Service resolution
-
-On its first connection, the client starts a `sysml-grpc` service if none was
-configured. It checks `$OPENSYSML_BINARY`, the shared cache, downloads the
-release it was built against, then checks `$PATH`. Release downloads are
-verified against the digest pinned in the package when one is available. A
-release of `opensysml` pins the five `sysml-grpc-*` binaries of its own release,
-stamped into its `release-digests.json` from the built binaries before the wheel
-is built, so installing a release and connecting needs no environment variable
-and no `sigstore` at run time. For another release, or one newer than the
-package's table, the client verifies the release's signed checksum manifest
-with `sigstore` and uses its digest; if that package is missing the download is
-refused, never taken unverified, and the error names the package and its
-install (`python -m pip install 'sigstore>=4.5.0,<5'`). A manifest that
-disagrees with a package pin is an integrity failure. Without a package pin or
-a digest from a verifiable signed manifest, the download is refused unless
-`OPENSYSML_ALLOW_UNPINNED_DOWNLOAD` opts into trusting a same-origin checksum.
-See the [service guide](https://opensysml.org/clients/python/service/) for
-cache ownership, offline behavior, trust configuration and external service
-setup.
+## The service
+
+The client talks to a `sysml-grpc` service. You do not have to install or
+start one: the first connection starts a private service for the current
+interpreter and stops it when the interpreter exits.
+
+To find the service binary, the client checks, in order:
+
+1. `$OPENSYSML_BINARY`, if set.
+2. The shared cache at `~/.opensysml/bin/sysml-grpc`.
+3. A download of the OpenSysML release this package was built against.
+4. A `sysml-grpc` on `$PATH`.
+
+A downloaded binary is verified against a SHA-256 digest shipped inside the
+package, so a normal `pip install opensysml` followed by `opensysml.connect()`
+needs no environment variables and no extra setup. Downloading another release
+is also verified, through its signed checksum manifest; an unverifiable download
+is refused rather than trusted.
+
+To use a service you run yourself, pass its address:
+
+```python
+model = opensysml.connect("localhost:50051").load("model.sysml")
+```
+
+The [service guide](https://opensysml.org/clients/python/service/) covers the
+cache, offline use, trust configuration and connecting to an external service.
 
 ## Documentation