docs(fifthandskip): instructions upgrade

- fix title header
- add missing package 'piscine'
- format indentation

subjects/fifthandskip/README.md

@@ -0,0 +1,45 @@
+## fifthandskip
+
+### Instructions
+
+Write a function `FifthAndSkip()` that takes a `string` and returns another `string`. The function separates every five characters of the `string` with a space and removes the sixth one.
+
+- If there are spaces in the middle of a word, ignore them and get the first character after the spaces until you reach a length of 5.
+- If the `string` is less than 5 characters returns `Invalid Output` followed by a newline `\n`.
+- If the `string` is empty return a newline `\n`.
+
+### Expected function
+
+```go
+func FifthAndSkip(str string) string {
+
+}
+```
+
+### Usage
+
+Here is a possible program to test your function:
+
+```go
+package main
+
+import (
+	"fmt"
+	"piscine"
+)
+
+func main() {
+	fmt.Print(piscine.FifthAndSkip("abcdefghijklmnopqrstuwxyz"))
+	fmt.Print(piscine.FifthAndSkip("This is a short sentence"))
+	fmt.Print(piscine.FifthAndSkip("1234"))
+}
+```
+
+And its output:
+
+```console
+$ go run . | cat -e
+abcde ghijk mnopq stuwx z$
+Thisi ashor sente ce$
+Invalid Output$
+```