docs: the Python package — install with maturin, h5py-style reading

README gains a Python section (maturin develop into a venv, a reading
example that was run against an h5py-written file, the supported types
and keys, what writing covers). The crate README says the same in more
detail. QUICKSTART showed clawhdf5.open()/read_f64(), which never
existed; it now shows File(...)[...].

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

docs/QUICKSTART.md

@@ -395,19 +395,22 @@ clawhdf5 --path agent.h5 snapshot backup_2026-03-19.h5
 Read HDF5 files from Python without libhdf5:
 
 ```bash
-pip install clawhdf5  # coming soon — build from source for now
-cd crates/clawhdf5-py && maturin develop
+# Not on PyPI yet: build from source into a virtualenv
+pip install maturin numpy
+cd crates/clawhdf5-py && maturin develop --release
 ```
 
 ```python
 import clawhdf5
 
-# Read
-f = clawhdf5.open("data.h5")
-temps = f.read_f64("temperatures")
-print(temps)  # [22.5, 23.1, 21.8]
+# Read (h5py-style)
+with clawhdf5.File("data.h5", "r") as f:
+    temps = f["temperatures"][:]
+    print(temps)  # [22.5 23.1 21.8]
 ```
 
+See `crates/clawhdf5-py/README.md` for the supported types and indexing.
+
 ---
 
 ## Common Patterns