(DOCSP-11269): Run selected lines from playground (mongodb#21)

* (DOCSP-11269): Run selected lines from playground

* copy edit

Author: jeff-allen-mongo

source/playgrounds.txt

@@ -46,6 +46,22 @@ To open a playground and begin interacting with your data:
 Your playground runs against the deployment specified in your
 :ref:`active connection <vsce-connect>`.
 
+Run a Playground
+----------------
+
+To run a playground, click the :guilabel:`Play Button` in VS Code's
+top navigation bar.
+
+Run Selected Lines of a Playground
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you select a section of your playground, you may optionally run only
+the selected portion. Your selection can consist of a single line or multiple lines.
+
+|vsce| shows the :guilabel:`Run Selected Lines from Playground` button
+immediately below your selected section. Click this button to test and
+troubleshoot specific lines or sections of your playground.
+
 Tutorials
 ---------