[mlir][linalg] Update OpDSL doc (NFC).

tree, MLIR must be build with Python bindings enabled

(`-DMLIR_ENALBE_BINDINGS_PYTHON=ON`). Then add the `python` directory in the

build tree to your `PYTHONPATH` environment variable (i.e. `export

PYTHONPATH=$PWD/build/python`). Optionally, use an installed MLIR package, if

available, to avoid building.

PYTHONPATH=$PWD/build/tools/mlir/python_packages/mlir_core`). Optionally, use an

installed MLIR package, if available, to avoid building.

```shell

# Dump the `core_named_ops.py` module as YAML.

python -m mlir.dialects.linalg.opdsl.dump_oplib .ops.core_named_ops

```

The tool is meant for use during both development and runtime, but not as a

build tool of the core compiler: in order to export static named op definitions

to be built as part of the compiler, the corresponding Linalg dialect YAML file

must be updated and reviewed. TODO: Develop a script to automate op updates to

these files.

Alternatively, run the `$PWD/build/bin/update_core_linalg_named_ops.sh` script,

which is available after building the `mlir-linalg-ods-gen` target. The tool is

meant for use during both development and runtime, but not as a build tool of

the core compiler: in order to export static named op definitions to be built as

part of the compiler, the corresponding Linalg dialect YAML file must be updated

and reviewed. TODO: Develop a script to automate op updates to these files.

## Language Guide