Updates to match the NEP

stringdtype/README.md

@@ -1,16 +1,17 @@
 # A dtype that stores pointers to strings
 
-This is a simple proof-of-concept dtype using the (as of early 2023) experimental
-[new dtype
-implementation](https://numpy.org/neps/nep-0041-improved-dtype-support.html) in
-NumPy.
+This is the prototype implementation of the variable-width UTF-8 string DType
+described in [NEP 55](https://numpy.org/neps/nep-0055-string_dtype.html).
+
+See the NEP for implementation details and usage examples. Full
+documentation will be written as before this code is merged into NumPy.
 
 ## Building
 
 Ensure Meson and NumPy are installed in the python environment you would like to use:
 
 ```
-$ python3 -m pip install meson meson-python build patchelf
+$ python3 -m pip install meson meson-python
 ```
 
 It is important to have the latest development version of numpy installed.
@@ -20,16 +21,35 @@ Nightly wheels work well for this purpose, and can be installed easily:
 $ pip install -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy
 ```
 
-Build with meson, create a wheel, and install it.
+You can install with `pip` directly, taking care to disable build isolation so
+the numpy nightly gets picked up at build time:
+
+```bash
+$ pip install -v . --no-build-isolation
+```
+
+If you want to work on the `stringdtype` code, you can build with meson,
+create a wheel, and install it.
 
 ```bash
 $ rm -r dist/
 $ meson build
 $ python -m build --wheel -Cbuilddir=build
+$ python -m pip install dist/path-to-wheel-file.whl
 ```
 
-Or simply install directly, taking care to install without build isolation:
+## Usage
+
+The dtype will not import unless you run python executable with
+the `NUMPY_EXPERIMENTAL_DTYPE_API` environment variable set:
 
 ```bash
-$ pip install -v . --no-build-isolation
+$ NUMPY_EXPERIMENTAL_DTYPE_API=1 python
+Python 3.11.3 (main, May  2 2023, 11:36:22) [GCC 11.3.0] on linux
+Type "help", "copyright", "credits" or "license" for more information.
+>>> from stringdtype import StringDType
+>>> import numpy as np
+>>> arr = np.array(["hello", "world"], dtype=StringDType())
+>>> arr
+array(['hello', 'world'], dtype=StringDType())
 ```