Add README for shared_pathways_service

Author: guptaaka

pathwaysutils/experimental/shared_pathways_service/README.md

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+# Shared Pathways Service
+
+Shared pathways service is a multi-tenant Pathways cluster with dedicated TPU
+resources. This eliminates the need for complex cloud setup, allowing you to
+get started from a familiar local environment (like a laptop or cloud VM) with
+minimal overhead: Just wrap your Python entrypoint in a
+`with isc_pathways.connect():` block!.
+
+## Requirements
+
+Make sure that your cluster is running the Resource Manager and Worker pods.
+If not, you can use [pw-service-example.yaml](yamls/pw-service-example.yaml).
+Make sure to modify the following values to deploy these pods:
+
+- A unique Jobset name for the cluster's Pathways pods
+- GCS bucket path
+- TPU type and topology
+- Number of slices
+
+These fields are highlighted in the YAML file with trailing comments for easier
+understanding.
+
+## Instructions
+
+1. Clone `pathwaysutils`.
+
+`git clone https://github.com/AI-Hypercomputer/pathways-utils.git`
+
+2. Import `isc_pathways.py` and move your workload under
+`with isc_pathways.connect()` statement. Refer to
+[run_connect_example.py](run_connect_example.py) for reference. Example code:
+
+```
+ from pathwaysutils.experimental.shared_pathways_service import isc_pathways
+
+ with isc_pathways.connect(
+     "my-cluster",
+     "my-project",
+     "region",
+     "gs://user-bucket",
+     "pathways-cluster-pathways-head-0-0.pathways-cluster:29001",
+     {"tpuv6e:2x2": 2},
+ ) as tm:
+   import jax.numpy as jnp
+   import pathwaysutils
+   import pprint
+
+   pathwaysutils.initialize()
+   orig_matrix = jnp.zeros(5)
+   ...
+```