DOCS: TCP route for Microsoft SQL (#3126)

* example TCP route for Microsoft SQL

* note pre-existing route on ms-sql example

docs/.vuepress/config.js

@@ -162,6 +162,7 @@ module.exports = {
               sidebarDepth: 0,
               children: [
                 "tcp/git",
+                "tcp/ms-sql",
                 "tcp/mysql",
                 "tcp/rdp",
                 "tcp/redis",

docs/docs/tcp/ms-sql.md

@@ -0,0 +1,49 @@
+---
+title: Microsoft SQL
+description: Tunnel Microsoft SQL connections through Pomerium
+---
+
+# Tunneled Microsoft SQL Connections
+
+This document explains how to connect to a Microsoft SQL database through an encrypted TCP tunnel. We use the `sqlcmd` command line utility, but the same tunnel can be used by GUI tools.
+
+::: tip
+This example assumes you've already [created a TCP route](/docs/tcp/readme.md#configure-routes) for this service.
+:::
+
+
+ ## Basic Connection
+
+ 1. Create a TCP tunnel, using either [`pomerium-cli`](/docs/releases.md#pomerium-cli) or the Pomerium Desktop client:
+
+    ::::: tabs
+    :::: tab pomerium-cli
+    ```bash
+    pomerium-cli tcp mssql.corp.example.com:1433 --listen :1433
+    ```
+
+    :::tip --listen
+    The `--listen` flag is optional. It lets you define what port the tunnel listens on locally. If not specified, the client will choose a random available port.
+    :::
+
+    ::::
+    :::: tab Pomerium Desktop
+    ![An example connection to a $SERVICE service from Pomerium Desktop](./img/desktop/example-mssql-connection.png)
+
+    :::tip Local Address
+    The **Local Address** field is optional. Using it defines what port the tunnel listens on locally. If not specified, Pomerium Desktop will choose a random available port.
+    :::
+
+    ::::
+    :::::
+
+1. Initiate your $SERVICE connection, pointing to `localhost`:
+
+    ```bash
+    /opt/mssql-tools/bin/sqlcmd -S localhost -U SA -P "YOURSTRONGPASSWORD"
+    ```
+
+## More Resources
+
+- [Quickstart: Run SQL Server container images with Docker](https://docs.microsoft.com/en-us/sql/linux/quickstart-install-connect-docker)
+- [Install the SQL Server command-line tools sqlcmd and bcp on Linux](https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-setup-tools)