Add license command

Author: willtheorangeguy

docs/COMMANDS.md

@@ -9,6 +9,7 @@ skip    Skips the current workout activity.
 end     Completes the workout and display full workout statistics.
 stats   Shows workout statistics at any point (does not work with the `skip` command).
 video   Opens the workout video assigned to each muscle group.
+license Shows the license. 
 help    Prints this help text.
 quit    Ends the program.
 ```
@@ -95,6 +96,10 @@ You are in the abs muscle group.
 The current time is: 14:33:04. 0:00:01.564038 has elapsed.
 ```
 
+### `license`
+
+Shows the GNU GPL v3 license text. The full license can be accessed in the `LICENSE.md` file. 
+
 ### `help`
 
 Prints a list of each of the available commands. Example: