Add doc.go (#8)

Author: johnfercher

README.md

@@ -8,6 +8,16 @@
 
 A generic unbalanced tree implementation, where you can define which node will be added to each node.
 
+## Installation
+
+* With `go get`:
+
+```bash
+go get -u github.com/johnfercher/tree
+```
+
+## Example
+
 ```golang
 package main
 

docs/doc.go

@@ -1 +1,64 @@
+/*
+# Tree
+
+A generic unbalanced tree implementation, where you can define which node will be added to each node.
+
+## Installation
+
+* With `go get`:
+
+```bash
+go get -u github.com/johnfercher/tree
+```
+
+## Example
+
+```golang
+package main
+
+import (
+
+	"fmt"
+
+	"github.com/johnfercher/tree/pkg/tree"
+
+)
+
+// nolint:gomnd,gocritic
+
+	func main() {
+		tr := tree.New[string]()
+
+		tr.AddRoot(tree.NewNode(0, "0.0"))
+
+		tr.Add(0, tree.NewNode(1, "0.1"))
+		tr.Add(0, tree.NewNode(2, "0.2"))
+
+		tr.Add(1, tree.NewNode(3, "1.3"))
+		tr.Add(1, tree.NewNode(4, "1.4"))
+
+		tr.Add(2, tree.NewNode(5, "2.5"))
+		tr.Add(2, tree.NewNode(6, "2.6"))
+
+		root, ok := tr.GetRoot()
+		fmt.Println(ok)         // true
+		fmt.Println(root.Get()) // 0, 0.0
+
+		node, ok := tr.Get(3)
+		fmt.Println(ok)         // true
+		fmt.Println(node.Get()) // 3, 1.3
+
+		structure, ok := tr.GetStructure()
+		fmt.Println(ok)        // true
+		fmt.Println(structure) // (NULL) -> (0), (0) -> (1),  (1) -> (3),  (1) -> (4),  (0) -> (2),  (2) -> (5),  (2) -> (6)
+
+		nodes, ok := tr.Backtrack(6)
+		fmt.Println(ok) // true
+		for _, node := range nodes {
+			fmt.Println(node.Get()) // 6, 2.6; 2, 0.2; 0, 0.0
+		}
+	}
+
+```
+*/
 package docs

pkg/tree/tree.go

@@ -62,7 +62,7 @@ func (t *Tree[T]) Backtrack(id int) ([]*Node[T], bool) {
 	return n.Backtrack(), true
 }
 
-// GetStructure retrieves Tree structure
+// GetStructure retrieves Tree structure.
 func (t *Tree[T]) GetStructure() ([]string, bool) {
 	if t.root == nil {
 		return nil, false