docs: add cqlsh instructions (#187)

* docs: add cqlsh instructions

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Co-authored-by: Atharva Moroney <[email protected]>

Author: mayurkale22

docs/cqlsh.md

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+# Integrating cqlsh with Spanner Cassandra Java Client
+
+This guide provides detailed instructions on setting up `cqlsh` to connect to the Spanner Cassandra Java Client.
+
+## Prerequisites
+
+- **cqlsh Version:** Ensure you have `cqlsh` versions from the branches `cassandra-4.0.13` or `cassandra-4.1.5`.
+- **Spanner Cassandra Java Client Setup:** Ensure the Spanner Cassandra Java Client is set up and running.
+
+## Setup Instructions
+
+>> NOTE: You may skip these instructions, if you already have `cqlsh` interface installed.
+
+### Option 1: Install cqlsh Directly
+
+#### Step 1: Download cqlsh
+
+Download the appropriate version of `cqlsh` by cloning the repository and following the instructions:
+
+- **cqlsh 4.0.13:**
+  ```sh
+  git clone https://github.com/apache/cassandra.git -b cassandra-4.0.13
+  cd cassandra/bin
+  ```
+
+- **cqlsh 4.1.5:**
+  ```sh
+  git clone https://github.com/apache/cassandra.git -b cassandra-4.1.5
+  cd cassandra/bin
+  ```
+
+#### Step 2: Configure cqlsh to Connect to the Spanner Cassandra Java Client (Optional)
+
+Edit the `cqlsh` configuration to point to the Spanner Cassandra Java Client:
+
+1. Open the `cqlshrc` configuration file. If it does not exist, create one in your home directory:
+   ```sh
+   nano ~/.cassandra/cqlshrc
+   ```
+
+2. Add the following configuration:
+   ```ini
+   [connection]
+   hostname = <java_client_hostname>
+   port = <java_client_port>
+   ```
+
+   Replace `<java_client_hostname>` and `<java_client_port>` with the appropriate values for your java client setup.
+
+#### Step 3: Launch cqlsh
+
+Launch `cqlsh` with the configured/default settings:
+```sh
+./cqlsh --protocol-version 4
+```
+
+Launch `cqlsh` with the custom hostname and port:
+```sh
+./cqlsh <java_client_hostname> <java_client_port> --protocol-version 4
+```
+
+Replace `<java_client_hostname>` and `<java_client_port>` with the appropriate values.
+
+### Option 2: Use Dockerized cqlsh
+
+#### Step 1: Install Docker
+
+Ensure Docker is installed on your machine. Follow the instructions on the [Docker website](https://docs.docker.com/get-docker/) to install Docker for your operating system.
+
+#### Step 2: Download and Run the Dockerized cqlsh
+
+Download the relevant Docker image and open a bash shell:
+```sh
+docker run -it nuvo/docker-cqlsh bash
+```
+
+#### Step 3: Find Your Machine’s IP Address
+
+Find the local IP address of the machine if the java client is running locally. For macOS, you can get the local machine IP address using:
+```sh
+ifconfig | grep "inet " | grep -v 127.0.0.1
+```
+
+#### Step 4: Connect to the Spanner Cassandra Java Client
+
+Open a bash shell in the Docker image:
+```sh
+docker run -it nuvo/docker-cqlsh bash
+```
+
+Connect to the Spanner Cassandra Java Client using your IP address and port:
+```sh
+cqlsh --protocol-version 4 '<your_ip_address>' <port>
+```
+
+Replace `<your_ip_address>` with the local IP address and `<port>` obtained in Step 3.
+
+### Option 3: Use pip
+
+To download and install `cqlsh` using `pip`, the Python package installer, one can use the following command:
+
+```sh
+pip install cqlsh
+```
+
+## Basic CRUD Operations
+
+**Insert:**
+```sql
+INSERT INTO keyspace_name.table_name (col1, col2, time, count) VALUES ('1234', 'check', '2024-06-13T05:19:16.882Z', 10);
+```
+
+**Select:**
+```sql
+SELECT * FROM keyspace_name.table_name WHERE col1 = '1234';
+```
+
+**Update:**
+```sql
+UPDATE keyspace_name.table_name SET count = 15 WHERE col1 = '1234' AND col2 = 'check' AND time = '2024-06-13T05:19:16.882Z';
+```
+
+**Delete:**
+```sql
+DELETE FROM keyspace_name.table_name WHERE col1 = '1234' AND col2 = 'check';
+```
+
+## Unsupported Queries
+
+DDL queries are not supported by the Spanner Cassandra Java Client when using `cqlsh`:
+
+- **Create Table:**
+  ```sql
+  CREATE TABLE keyspace_name.table_name (id UUID PRIMARY KEY, name text);
+  ```
+
+- **Drop Table:**
+  ```sql
+  DROP TABLE keyspace_name.table_name;
+  ```
+
+- **Describe Table:**
+  ```sql
+  DESCRIBE TABLE keyspace_name.table_name;
+  ```
+