Add Gradle instructions to custom SQL database guide

docs/StardustDocs/topics/readSqlFromCustomDatabase.md

@@ -2,17 +2,28 @@
 
 # How to Extend DataFrame Library for Custom SQL Database Support: Example with HSQLDB
 
-This guide demonstrates how advanced users can extend the Kotlin DataFrame library to support a custom SQL database, using HSQLDB as an example. By following these steps, you will be able to integrate your custom database into the DataFrame library, allowing for seamless DataFrame creation, manipulation, and querying.
+This guide demonstrates how advanced users can extend the Kotlin DataFrame library to support a custom SQL database, 
+using HSQLDB as an example. By following these steps, 
+you will be able to integrate your custom database into the DataFrame library, 
+allowing for seamless DataFrame creation, manipulation, and querying.
+
+This guide is intended for Gradle projects, 
+but the experience will be similar in Kotlin Notebooks, 
+as demonstrated in this [Kotlin DataFrame SQL Example](https://github.com/zaleslaw/KotlinDataFrame-SQL-Examples/blob/master/notebooks/customdb.ipynb).
 
 ---
 
 ## Prerequisites
 
 1. **Create a Gradle Project**:  
 
-Add the following dependencies to your `build.gradle.kts`:
+Add the following dependencies and dataframe plugin to your `build.gradle.kts`:
 
 ```kotlin
+plugins {
+    id("org.jetbrains.kotlinx.dataframe") version "$dataframe_version"
+}
+
 dependencies {
     implementation("org.jetbrains.kotlinx:dataframe:$dataframe_version")
     implementation("org.hsqldb:hsqldb:$version")
@@ -39,14 +50,6 @@ To enable HSQLDB integration, implement a custom `DbType` by overriding required
 **Create the HSQLDB Type**
 
 ```kotlin
-import org.jetbrains.kotlinx.dataframe.io.TableColumnMetadata
-import org.jetbrains.kotlinx.dataframe.io.TableMetadata
-import org.jetbrains.kotlinx.dataframe.io.db.DbType
-import org.jetbrains.kotlinx.dataframe.schema.ColumnSchema
-import java.sql.ResultSet
-import java.util.Locale
-import kotlin.reflect.KType
-
 /**
  * Represents the HSQLDB database type.
  *
@@ -87,10 +90,9 @@ public object HSQLDB : DbType("hsqldb") {
 **Defining Helper Functions**
 
 Define utility functions to manage database connections and tables.
+For example purposes, we create a small function that can populate the table with a schema and some sample data.
 
 ```kotlin
-import java.sql.Connection
-
 const val URL = "jdbc:hsqldb:hsql://localhost/testdb"
 const val USER_NAME = "SA"
 const val PASSWORD = ""
@@ -102,7 +104,7 @@ fun removeTable(con: Connection): Int {
 }
 
 fun createAndPopulateTable(con: Connection) {
-    var stmt = con.createStatement()
+    val stmt = con.createStatement()
     stmt.executeUpdate(
         """CREATE TABLE IF NOT EXISTS orders (
                         id INT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
@@ -148,9 +150,9 @@ fun main() {
     DriverManager.getConnection(URL, USER_NAME, PASSWORD).use { con ->
         createAndPopulateTable(con)
 
-        val df = con.readDataFrame("SELECT * FROM orders", dbType = HSQLDB).rename {
-            all()
-        }.into { it.name.lowercase(Locale.getDefault()).toCamelCaseByDelimiters(DELIMITERS_REGEX) }
+        val df = con
+            .readDataFrame("SELECT * FROM orders", dbType = HSQLDB)
+            .rename { all() }.into { it.name.lowercase(Locale.getDefault()).toCamelCaseByDelimiters(DELIMITERS_REGEX) }
             .cast<Orders>(verify = true)
 
         df.filter { it.price > 800 }.print()
@@ -160,7 +162,7 @@ fun main() {
 }
 ```
 
-Running the above main function will output filtered rows from the `orders` table where `price > 800`. 
+Running the `main` function above will output filtered rows from the `orders` table where `price > 800`. 
 
 It will also demonstrate how to define and use custom SQL database extensions in the DataFrame library.