feat(piscine-go): add README.md for new go exercise podiumposition

subjects/podiumposition/README.md

@@ -0,0 +1,38 @@
+## podiumposition
+
+### Instructions
+
+A F1 race just finished and the commentator is calling the finishing positions incorrectly.
+Help to fix this before the contestants arrive at the podium by providing the commentator with the correct podium position.
+
+Write a function `PodiumPosition` that accepts an array of arrays as a `string` and returns the competitor positions correctly.
+
+### Expected function
+
+```go
+func PodiumPosition(podium[][] string) [][]string {
+
+}
+```
+
+### Usage
+
+Here is a possible program to test your function:
+
+```go
+package main
+
+import "fmt"
+
+func main() {
+    position := [][]string{{"4th Place"}, {"3rd Place"}, {"2nd Place"}, {"1st Place"}}
+    	fmt.Println(PodiumPosition(position))
+}
+```
+
+And its output:
+
+```go
+$ go run . | cat -e
+[[1st Place] [2nd Place] [3rd Place] [4th Place]]$
+```