Add notice about "Unique" solutions

solution/README.md

@@ -12,12 +12,14 @@
 | 3 | 5pt | What is the largest Perimeter of a Group?  | Integer | 22 |
 | 4 | 5pt | Which 2 Shapes can create a square Group?  | Letter list | L0,P5 [image example](https://static.mathigon.org/cms/2aeb6180e05938d28d8659e07133617d.png) |
 | 5 | 10pt | Which 2-Shape Groups look the same (on a 2d representation) with any other 2-Shape Group? | Letter list | [image](https://people.rit.edu/mecsma/Professional/Puzzles/Pentominoes/P-A%20Images/image21.gif) |
-| 6 | 10pt | How many unique solutions can you find for a 3×20 Canvas? | Integer | 2, [source](https://isomerdesign.com/Pentomino/3x20/index.html) |
+| 6 | 10pt | How many unique\* solutions can you find for a 3×20 Canvas? | Integer | 2, [source](https://isomerdesign.com/Pentomino/3x20/index.html) |
 | 7 | 10pt | How many unique solutions can you find for a 5×3 Canvas? | Integer | 7, [source](https://isomerdesign.com/Pentomino/5x3/index.html) |
 | 8 | 10pt | How many unique solutions can you find for a 4×15 Canvas? | Integer | 368, [source](https://isomerdesign.com/Pentomino/4x15/index.html) |
 | 9 | 20pt | How many unique solutions can you find for a 3×21 Canvas with 3 black holes as seen on the image below? !["3x21 Canvas with 3 black holes"](../images/canvas_3x21_3_black.png) | Integer | 6, [source](https://isomerdesign.com/Pentomino/3x21d) |
 | 10 | 20pt | Which Shapes can be put together to make a copy of the P-shape which is bigger from the original piece. | Letter list | `ZVVV ZZZV NNZV PNNN PP PP` [image](https://people.rit.edu/mecsma/Professional/Puzzles/Pentominoes/P-A%20Images/image23.gif) |
 
+\* Unique solutions: Where the answer is not a result of a simple rotation or flip of the whole (solved) canvas. If we do so all the answers provided here should be multiplied with the number `4`.
+
 > **Total: 100pts**.
 
 ### C. Graphical User Interface (GUI)