docs: refactor search example (#27)

Author: sykp241095

examples/embedding_search/README.md renamed to examples/search/README.md

@@ -45,10 +45,31 @@ source .venv/bin/activate
 pip install -r reqs.txt
 ```
 
-**Step3**: Run the Streamlit app
+**Step3**: Set up environment to connect to storage
+If you are using TiDB Cloud, you'd better set up the environment variable `DATABASE_URL` to connect to the TiDB Cloud database. You can find the connection string in the [TiDB Cloud console](https://tidbcloud.com/).
+
+```bash
+cat > .env <<EOF
+DATABASE_URL="mysql+pymysql://<username>:<password>@<host>:4000/test?ssl_verify_cert=true&ssl_verify_identity=true"
+EOF
+```
+
+If you are using a local TiDB server, you can set up the environment variable like this:
+
+```bash
+cat > .env <<EOF
+TIDB_HOST=localhost
+TIDB_PORT=4000
+TIDB_USERNAME=root
+TIDB_PASSWORD=
+TIDB_DATABASE=test
+EOF
+```
+
+**Step4**: Run the Streamlit app
 
 ```bash
 streamlit run main.py
 ```
 
-**Step4**: open the browser and visit `http://localhost:8501`
+**Step5**: open the browser and visit `http://localhost:8501`