Update README.md

Author: aswinkarthik

README.md

@@ -2,9 +2,19 @@
 
 Inspired from [Lodash](https://github.com/lodash/lodash) for golang
 
-# Functions
+## Why?
 
-## Map
+I did not like most map/reduce implementations that returned an `interface{}` which had to be typecasted. This library follows the concept of how `json.Marshal` works. Create an output variable **outside** the functions and pass a **pointer reference** to it, so it can be **set**.
+This library heavily makes use of `reflect` package and hence will have an **impact on performance**. Use it with care. All functions have **validations** on how mapper function/predicate functions should be written. So even if we lose out on compile time validation, the library still **does not panic** if it does not know how to handle an argument passed to it.
+
+## Available Functions
+
+1. [Map](#Map)
+2. [Filter](#Filter)
+
+## Usages
+
+### Map
 
 Map applies a mapper function on each element of an input and sets it in output. 
 
@@ -13,9 +23,9 @@ _Primitive types_
 ```go
 func main() {
 	input := []int{1, 2, 3, 4, 5}
-	output := make([]int, 0)
+	var output []int
 
-	_ = godash.Map(input, &output, func(el int) int {
+	godash.Map(input, &output, func(el int) int {
 		return el * el
 	})
 
@@ -36,12 +46,45 @@ func main() {
 		{Name: "John", Age: 22},
 		{Name: "Doe", Age: 23},
 	}
-	output := make([]string, 0)
+	var output []string
 
-	_ = godash.Map(input, &output, func(person Person) string {
+	godash.Map(input, &output, func(person Person) string {
 		return person.Name
 	})
 
 	fmt.Println(output) // prints John Doe
 }
 ```
+
+### Filter
+
+Filter out elements that fail the predicate
+
+```go
+func main() {
+	input := []int{1, 2, 3, 4, 5}
+	var output []int
+
+	godash.Filter(input, &output, func(el int) bool {
+		return bool % 2 == 0
+	})
+
+	fmt.Println(output) // prints 2 4
+}
+```
+
+```go
+func main() {
+	input := []Person{
+		{Name: "John", Age: 20},
+		{Name: "Doe", Age: 30},
+	}
+	var output []string
+
+	godash.Filter(input, &output, func(person Person) string {
+		return person.Age > 25
+	})
+
+	fmt.Println(output) // prints {John 20}
+}
+```