Merge pull request #522 from pietdaniel/master

[documentation] add docs on port configuration

Author: barbaravaldez

doc/usage_guide.md

@@ -78,6 +78,12 @@ Connect to a server, a specific database, and with a username. -S -d and -U are
 mssql-cli -S localhost -d AdventureWorks -U sa
 ```
 
+If the server is using a nonstandard port (1433) you can specify a port via the following invocation:
+
+```bash
+mssql-cli -S "localhost,42069" -d AdventureWorks -U sa
+```
+
 ### Exit mssql-cli 
 Press **Ctrl+D** or type `quit`.
 
@@ -283,4 +289,4 @@ pager=pypager
 ```
 
 ## Troubleshooting
-If you encounter any issues, see the [troubleshooting](troubleshooting_guide.md) section for known issues and workarounds.
+If you encounter any issues, see the [troubleshooting](troubleshooting_guide.md) section for known issues and workarounds.