doc: add document for AppendIfAbsent function

docs/slice.md

@@ -20,6 +20,7 @@ import (
 <div STYLE="page-break-after: always;"></div>
 
 ## Index
+- [AppendIfAbsent](#AppendIfAbsent)
 - [Contain](#Contain)
 - [ContainSubSlice](#ContainSubSlice)
 - [Chunk](#Chunk)
@@ -69,6 +70,33 @@ import (
 
 ## Documentation
 
+### <span id="AppendIfAbsent">AppendIfAbsent</span>
+<p>If slice doesn't contain the value, append it to the slice.</p>
+
+<b>Signature:</b>
+
+```go
+func AppendIfAbsent[T comparable](slice []T, value T) []T
+```
+<b>Example:</b>
+
+```go
+import (
+	"fmt"
+	"github.com/duke-git/lancet/v2/slice"
+)
+
+func main() {
+	strs := []string{"a", "b"}
+	res1 := slice.AppendIfAbsent(strs, "a")
+	fmt.Println(res1) //[]string{"a", "b"}
+
+	res2 := slice.AppendIfAbsent(strs, "cannot")
+	fmt.Println(res2"}
+}
+```
+
+
 ### <span id="Contain">Contain</span>
 <p>Check if the value is in the slice or not.</p>
 

docs/slice_zh-CN.md

@@ -20,6 +20,7 @@ import (
 <div STYLE="page-break-after: always;"></div>
 
 ## 目录
+- [AppendIfAbsent](#AppendIfAbsent)
 - [Contain](#Contain)
 - [ContainSubSlice](#ContainSubSlice)
 - [Chunk](#Chunk)
@@ -69,6 +70,34 @@ import (
 
 ## 文档
 
+### <span id="AppendIfAbsent">AppendIfAbsent</span>
+<p>当前切片中不包含值时，将该值追加到切片中</p>
+
+<b>函数签名:</b>
+
+```go
+func AppendIfAbsent[T comparable](slice []T, value T) []T
+```
+<b>例子:</b>
+
+```go
+import (
+	"fmt"
+	"github.com/duke-git/lancet/v2/slice"
+)
+
+func main() {
+	strs := []string{"a", "b"}
+	res1 := slice.AppendIfAbsent(strs, "a")
+	fmt.Println(res1) //[]string{"a", "b"}
+
+	res2 := slice.AppendIfAbsent(strs, "cannot")
+	fmt.Println(res2"}
+}
+```
+
+
+
 ### <span id="Contain">Contain</span>
 <p>判断slice是否包含value</p>