fix link to space invaders instructions

Author: pulkitkrishna00

docs/computer-science/program-design/spd/index.md

@@ -22,7 +22,7 @@ Alternative Links (Not recommended):
 
 - The course does not have a homepage on Edx, but don't worry about it. Open the [link](https://learning.edx.org/course/course-v1:UBCx+SPD1x+2T2015) given above, log in (if you are not logged in) and then enroll in the course.
 - Work through Week 1A to Week 6A as given in the course overview. Watch the videos, do the exercises, and then solve the problems from the problem bank.
-- After you complete, Week 6A, do the [space invaders problem](https://github.com/BorrProject/spd-starters/blob/main/final/space-invaders-starter.rkt). You can find further instructions here: [Space Invaders Instructions](./space-invaders-instructions.png). You can watch a sample run of the game [here](https://youtube.com/video/7dEciy3f7UU).
+- After you complete, Week 6A, do the [space invaders problem](https://github.com/BorrProject/spd-starters/blob/main/final/space-invaders-starter.rkt). You can find further instructions here: [Space Invaders Instructions](./space-invaders.md). You can watch a sample run of the game [here](https://youtube.com/video/7dEciy3f7UU).
 - Then, work through Week 6B onwards. Watch the videos, do the exercises, and then solve the problems from the problem bank.
 - After that, watch the extra videos in [this playlist](https://www.youtube.com/playlist?list=PL6NenTZG6KrqdcyTwGf09uBxjI5pbXuT7).
 - After you complete all the modules in the course, do the [TA solver problem](https://github.com/BorrProject/spd-starters/blob/main/final/ta-solver-starter.rkt). You will find the instructions in the starter file.

docs/computer-science/program-design/spd/space-invaders-instructions.png

@@ -0,0 +1,16 @@
+# Space Invaders
+
+In this project, you will complete the design of the classic arcade game Space Invaders. If you've never played it before, you can get an idea of how it works [here](https://youtube.com/video/7dEciy3f7UU).
+
+There are many different versions of Space Invaders. For this project, your Space Invaders game should have the following behaviour:
+
+- The tank should move right and left at the bottom of the screen when you press the arrow keys. If you press the left arrow key, it will continue to move left at a constant speed until you press the right arrow key.
+- The tank should fire missiles straight up from its current position when you press the space bar.
+- The invaders should appear randomly along the top of the screen and move at a 45 degree angle. When they hit a wall they will bounce off and continue at a 45 degree angle in the other direction.
+- When an invader reaches the bottom of the screen, the game is over.
+
+This is an example of what the game should look like during play. The arrows have been added on to show you how the different parts of the game move.
+
+![Space Invaders screenshot](./space-invaders.webp)
+
+Designing this program will require many of the things you have learned throughout the course till now, and it will be the largest program you have worked on. Before downloading the starter file, take some time to become acquainted with the game, and complete the domain analysis for the program.