docs: 📝 Update docs

docs/en/help/escrcpy.md

@@ -105,4 +105,8 @@ This might be due to Chinese or special characters in the installation path. Ple
 
 ```shell
 sudo chmod 4755 /opt/Escrcpy/chrome-sandbox
-```
+```
+
+### Black edges appear after resizing the casting window
+
+If black edges appear after resizing the casting window, simply **double-click the black edge area** and it will automatically hide.

docs/zhHans/help/escrcpy.md

@@ -100,4 +100,8 @@
 
 ```shell
 sudo chmod 4755 /opt/Escrcpy/chrome-sandbox
-```
+```
+
+### 调整投屏窗口大小后出现黑边
+
+当调整投屏窗口尺寸后出现黑边时，只需双击黑边区域即可让其自动隐藏。