Instructions for accessing a command terminal on Mac (#13672)

* Instructions for accessing a command terminal on Mac

@Rick-Anderson Here is the new file we discussed. 
/cc: @anangaur

* Update mac-terminal-access.md

aspnetcore/includes/mac-terminal-access.md

@@ -0,0 +1,18 @@
+### Accessing a Command Terminal on Visual Studios for Mac
+
+Accessing a command terminal on Mac for the first time requires the following setting configurations:
+
+* Navigate to **System Preferences > Keyboard > Shortcuts > Services**.
+* Under **Files and Folders**, verify **New Terminal at Folder** is selected.
+
+The preceding instructions enable access a command terminal two ways: from inside **Visual Studios** or from **Finder**. 
+
+#### To access a command terminal from Visual Studio for Mac:
+
+* Right click the project name.
+* Navigate to **Tools > Open in Terminal**.
+
+#### To access a command terminal from Finder:
+
+* Right click the desired folder.
+* At the bottom of the list, select **New Terminal at Folder**.