doc: add doc for ZipAppendEntry

docs/fileutil.md

@@ -37,6 +37,7 @@ import (
 -   [ReadFileToString](#ReadFileToString)
 -   [ReadFileByLine](#ReadFileByLine)
 -   [Zip](#Zip)
+-   [ZipAppendEntry](#ZipAppendEntry)
 -   [UnZip](#UnZip)
 -   [IsZipFile](#IsZipFile)
 -   [FileSize](#FileSize)
@@ -476,6 +477,34 @@ func main() {
 }
 ```
 
+### <span id="ZipAppendEntry">ZipAppendEntry</span>
+
+<p>Append a single file or directory by fpath to an existing zip file.</p>
+
+<b>Signature:</b>
+
+```go
+func ZipAppendEntry(fpath string, destPath string) error 
+```
+
+<b>Example:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/v2/fileutil"
+)
+
+func main() {
+    err := fileutil.ZipAppendEntry("./test.txt", "./test.zip")
+    if err != nil {
+        fmt.Println(err)
+    }
+}
+```
+
 ### <span id="UnZip">UnZip</span>
 
 <p>Unzip the file and save it to dest path.</p>