Add exercise `matrix_display`s subject

subjects/insertion_sort/README.md

@@ -19,8 +19,6 @@ Here is a visual example of sorting a slice step by step using the insertion sor
 
 - Implement the algorithm insertion sort by creating a function `insertion_sort(slice, steps)` that executes the iterations of the algorithm the number of steps indicated by the parameter `steps`. See the [Usage](#usage) for more information.
 
-### Notion
-
 ### Expected Function
 
 ```rust

subjects/matrix_display/README.md

@@ -0,0 +1,44 @@
+## matrix_display
+
+### Instructions
+
+Use the Matrix struct given in the [expected struct](#expected-functions-and-struct) and implement the `std::fmt::Display` trait so it prints the matrix like in the [usage](#usage).
+
+You will also have to implement the associated function `new` that creates a matrix from a slice of slices.
+
+### Expected Functions and Struct
+
+```rust
+pub struct Matrix(pub Vec<Vec<i32>>);
+
+pub fn new(slice: &[&[i32]]) -> Self {
+}
+
+use std::fmt;
+
+impl fmt::Display for Matrix {
+}
+```
+
+### Usage
+
+Here is a possible program to test your function
+
+```rust
+use matrix_display::*;
+
+fn main() {
+	let matrix = Matrix::new(&[&[1, 2, 3], &[4, 5, 6], &[7, 8, 9]]);
+	println!("{}", matrix);
+}
+```
+
+And it's output:
+
+```console
+student@ubuntu:~/[[ROOT]]/test$ cargo run
+(1 2 3)
+(4 5 6)
+(7 8 9)
+student@ubuntu:~/[[ROOT]]/test$
+```