Added hello world program for C# YSQL (#136)

Author: sibtayshah

content/latest/develop/build-apps/csharp.md

@@ -19,10 +19,20 @@ menu:
       YCQL
     </a>
   </li>
+  <li>
+    <a href="#ysql" class="nav-link" id="ysql-tab" data-toggle="tab" role="tab" aria-controls="ysql" aria-selected="true">
+      <i class="icon-postgres" aria-hidden="true"></i>
+      YSQL
+    </a>
+  </li>
 </ul>
 
 <div class="tab-content">
   <div id="ycql" class="tab-pane fade show active" role="tabpanel" aria-labelledby="ycql-tab">
     {{% includeMarkdown "ycql/csharp.md" /%}}
   </div>
+  <div id="ysql" class="tab-pane fade show active" role="tabpanel" aria-labelledby="ysql-tab">
+    {{% includeMarkdown "ysql/csharp.md" /%}}
+  </div>
+
 </div>

content/latest/develop/build-apps/ysql/csharp.md

@@ -0,0 +1,87 @@
+## Prerequisites
+
+This tutorial assumes that you have:
+
+- installed YugaByte DB, created a universe and are able to interact with it using the YSQL shell. If not, please follow these steps in the [ysql guide](../../../api/ysql/).
+- installed Visual Studio
+
+## Writing a HelloWorld C# app
+
+In your Visual Studio create a new Project and choose Console Application as template. Follow the instructions to save the project.
+
+### Install YSQL C# driver
+To install the driver in your Visual Studio project
+<ol>
+  <li>Open your Project Solution View.</li>
+  <li>Right-click on Packages and click Add Packages.</li>
+  ![Add Package](/images/develop/client-drivers/csharp/visual-studio-add-package.png) 
+  <li>Search for Npgsql and click Add Package.</li>
+  ![Search Package](/images/develop/client-drivers/csharp/visual-studio-search-ngpsql-package.png)
+</ol>
+
+### Copy the contents below to your `Program.cs` file.
+
+```cs
+using System;
+using Npgsql;
+
+namespace YugaByte_CSharp_Demo
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            NpgsqlConnection conn = new NpgsqlConnection("host=localhost;port=5433;database=yb_demo;user id=postgres;password=");
+
+            try
+            {
+                conn.Open();
+
+                NpgsqlCommand empCreateCmd = new NpgsqlCommand("CREATE TABLE employee (id int PRIMARY KEY, name varchar, age int, language varchar);", conn);
+                empCreateCmd.ExecuteNonQuery();
+                Console.WriteLine("Created table Employee");
+
+                NpgsqlCommand empInsertCmd = new NpgsqlCommand("INSERT INTO employee (id, name, age, language) VALUES (1, 'John', 35, 'CSharp');", conn);
+                int numRows = empInsertCmd.ExecuteNonQuery();
+                Console.WriteLine("Inserted data (1, 'John', 35, 'CSharp')");
+
+                NpgsqlCommand empPrepCmd = new NpgsqlCommand("SELECT name, age, language FROM employee WHERE id = @EmployeeId", conn);
+                empPrepCmd.Parameters.Add("@EmployeeId", NpgsqlTypes.NpgsqlDbType.Integer);
+
+                empPrepCmd.Parameters["@EmployeeId"].Value = 1;
+                NpgsqlDataReader reader = empPrepCmd.ExecuteReader();
+
+                Console.WriteLine("Query returned:\nName\tAge\tLanguage"); 
+                while (reader.Read())
+                {
+                    Console.WriteLine("{0}\t{1}\t{2}", reader.GetString(0), reader.GetInt32(1), reader.GetString(2));
+                }
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine("Failure: " + ex.Message);
+            }
+            finally
+            {
+                if (conn.State != System.Data.ConnectionState.Closed)
+                {
+                    conn.Close();
+                }
+            }
+        }
+    }
+}
+```
+
+### Running the C# app
+Run the C# app from menu select `Run -> Start Without Debugging`
+
+You should see the following as the output.
+
+```
+Created table Employee
+Inserted data (1, 'John', 35, 'CSharp')
+Query returned:
+Name	Age	Language
+John	35	CSharp
+```