docs(upload): documentation for download function (#362)

* feat: documentation for download func.

* fix: linguitic and header type changes

plugins/upload/README.md

@@ -1,6 +1,7 @@
 ![plugin-upload](banner.png)
 
 Upload files from disk to a remote server over HTTP.
+Download files from a remote HTTP server to disk.
 
 ## Install
 
@@ -54,10 +55,21 @@ Afterwards all the plugin's APIs are available through the JavaScript guest bind
 import { upload } from 'tauri-plugin-upload-api'
 
 upload(
-    'https://example.com/file-upload'
-    './path/to/my/file.txt'
-    (progress, total) => console.log(`Downloaded ${progress} of ${total} bytes`) // a callback that will be called with the upload progress
-    { 'ContentType': 'text/plain' } // optional headers to send with the request
+    'https://example.com/file-upload',
+    './path/to/my/file.txt',
+    (progress, total) => console.log(`Uploaded ${progress} of ${total} bytes`), // a callback that will be called with the upload progress
+    { 'Content-Type': 'text/plain' } // optional headers to send with the request
+)
+```
+
+```javascript
+import { download } from "tauri-plugin-upload-api";
+
+download(
+    'https://example.com/file-download-link',
+    './path/to/save/my/file.txt',
+    (progress, total) => console.log(`Downloaded ${progress} of ${total} bytes`), // a callback that will be called with the download progress
+    { 'Content-Type': 'text/plain' } // optional headers to send with the request
 )
 ```