Update README with example usage

Author: dnaeon

README.md

@@ -5,7 +5,8 @@
 [![Go Report Card](https://goreportcard.com/badge/gopkg.in/dnaeon/go-binarytree.v1)](https://goreportcard.com/report/gopkg.in/dnaeon/go-binarytree.v1)
 [![codecov](https://codecov.io/gh/dnaeon/go-binarytree/branch/v1/graph/badge.svg)](https://codecov.io/gh/dnaeon/go-binarytree)
 
-A simple implementation of [Binary Trees](https://en.wikipedia.org/wiki/Binary_tree) in Go.
+A simple, generic implementation of [Binary
+Trees](https://en.wikipedia.org/wiki/Binary_tree) in Go.
 
 ![Example Binary Tree](./images/binarytree.svg)
 
@@ -19,7 +20,134 @@ go get -v gopkg.in/dnaeon/go-binarytree.v1
 
 ## Usage
 
-See the included [test cases](./binarytree_test.go) for some examples.
+The following example builds a simple binary tree with 7 nodes, and
+performs _in-_, _pre-_, _post-_ and _level-order_ walking of the tree
+(error handling is omitted for simplicity).
+
+``` go
+package main
+
+import (
+	"fmt"
+
+	"gopkg.in/dnaeon/go-binarytree.v1"
+)
+
+func main() {
+	root := binarytree.NewNode(10)
+	five := root.InsertLeft(5)
+	twenty := root.InsertRight(20)
+	five.InsertLeft(9)
+	five.InsertRight(18)
+	twenty.InsertLeft(3)
+	twenty.InsertRight(7)
+
+	fmt.Printf("height of tree: %d\n", root.Height())
+	fmt.Printf("size of the tree: %d\n", root.Size())
+	fmt.Printf("tree is balanced: %t\n", root.IsBalancedTree())
+	fmt.Printf("tree is complete: %t\n", root.IsCompleteTree())
+	fmt.Printf("tree is perfect: %t\n", root.IsPerfectTree())
+
+	// Function to be called while walking the tree, which simply
+	// prints the values of each visited node
+	walkFunc := func(n *binarytree.Node[int]) error {
+		fmt.Printf("%d ", n.Value)
+		return nil
+	}
+
+	fmt.Printf("in-order values: ")
+	root.WalkInOrder(walkFunc)
+	fmt.Println()
+
+	fmt.Printf("pre-order values: ")
+	root.WalkPreOrder(walkFunc)
+	fmt.Println()
+
+	fmt.Printf("post-orer values: ")
+	root.WalkPostOrder(walkFunc)
+	fmt.Println()
+
+	fmt.Printf("level-order values: ")
+	root.WalkLevelOrder(walkFunc)
+	fmt.Println()
+}
+```
+
+Running above example produces the following output.
+
+``` shell
+height of tree: 2
+size of the tree: 7
+tree is balanced: true
+tree is complete: true
+tree is perfect: true
+in-order values: 9 5 18 10 3 20 7 
+pre-order values: 10 5 9 18 20 3 7 
+post-orer values: 9 18 5 3 7 20 10 
+level-order values: 10 5 20 9 18 3 7 
+```
+
+The following example generates the [Dot
+representation](https://en.wikipedia.org/wiki/DOT_(graph_description_language))
+of the binary tree and prints it to the standard output.
+
+``` go
+package main
+
+import (
+	"os"
+
+	"gopkg.in/dnaeon/go-binarytree.v1"
+)
+
+func main() {
+	root := binarytree.NewNode(10)
+	five := root.InsertLeft(5)
+	twenty := root.InsertRight(20)
+	five.InsertLeft(9)
+	five.InsertRight(18)
+	twenty.InsertLeft(3)
+	twenty.InsertRight(7)
+
+	root.WriteDot(os.Stdout)
+}
+```
+
+Running above example produces an output similar to this one.
+
+``` shell
+digraph {
+        node [color=lightblue fillcolor=lightblue fontcolor=black shape=record style="filled, rounded"]
+        824634441792 [label="<l>|<v> 10|<r>" ]
+        824634441792:l -> 824634441856:v
+        824634441792:r -> 824634441920:v
+        824634441856 [label="<l>|<v> 5|<r>" ]
+        824634441856:l -> 824634441984:v
+        824634441856:r -> 824634442048:v
+        824634441984 [label="<l>|<v> 9|<r>" ]
+        824634442048 [label="<l>|<v> 18|<r>" ]
+        824634441920 [label="<l>|<v> 20|<r>" ]
+        824634441920:l -> 824634442112:v
+        824634441920:r -> 824634442176:v
+        824634442112 [label="<l>|<v> 3|<r>" ]
+        824634442176 [label="<l>|<v> 7|<r>" ]
+}
+```
+
+The generated representation can be rendered using
+[graphviz](https://graphviz.org/), e.g.
+
+``` shell
+dot -Tsvg /path/to/file.dot -o /tmp/to/file.svg
+```
+
+When building a binary tree with user-defined types such as structs,
+make sure that you also implement the
+[fmt.Stringer](https://pkg.go.dev/fmt#Stringer) interface for your
+type, so that Dot generation works properly.
+
+Make sure to check the included [test cases](./binarytree_test.go) for
+additional examples.
 
 ## Tests