add readme and first example code

Adding a short description of the project to the readme file for better display on GitHub.
Also adding a first example how to use go module by using `GenerateRoundRobinTournamentMatchesByNumber()`.

README.md

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+# round robin tournament
+
+This is a golang module which will provide functions to generate a 2d slice of string containing matches of given teams.
+The matches will be generated using the [round-robin tournament](https://en.wikipedia.org/wiki/Round-robin_tournament).
+Every team will play against every other team.
+
+## example
+
+The following golang function call will create the 2d slice of strings above.
+```go
+GenerateRoundRobinTournamentMatchesByNumber(4)
+```
+
+```
+[
+  [Team 1 Team 2]
+  [Team 3 Team 4]
+  [Team 1 Team 4]
+  [Team 2 Team 3]
+  [Team 1 Team 3]
+  [Team 4 Team 2]
+]
+```
+
+You will find other examples in [example](example) directory.

example/example_bynumber.go

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+package main
+
+import (
+	"fmt"
+
+	"github.com/taskmedia/roundrobintournament"
+)
+
+func main() {
+	matches := roundrobintournament.GenerateRoundRobinTournamentMatchesByNumber(4)
+
+	for i, match := range matches {
+		fmt.Printf("match #%d: %s : %s\n", i+1, match[0], match[1])
+	}
+}