feat: change screenshot format to png

Close #102

QtScrcpy/device/device.cpp

@@ -368,10 +368,10 @@ bool Device::saveFrame(const AVFrame* frame)
     }
     QDateTime dateTime = QDateTime::currentDateTime();
     QString fileName = dateTime.toString("_yyyyMMdd_hhmmss_zzz");
-    fileName = Config::getInstance().getTitle() + fileName + ".jpg";
+    fileName = Config::getInstance().getTitle() + fileName + ".png";
     QDir dir(fileDir);
     absFilePath = dir.absoluteFilePath(fileName);
-    ret = rgbImage.save(absFilePath);
+    ret = rgbImage.save(absFilePath, "PNG", 100);
     if (!ret) {
         return false;
     }

README.md

@@ -160,6 +160,7 @@ Note: it is not necessary to keep you Android device connected via USB after you
 - Display Android device screens in real time
 - Real-time mouse and keyboard control of Android devices
 - Screen recording
+- Screenshot to png
 - Wireless connection
 - Supports up to 16 device connections (the number can be higher if your PC performance allows. You need to compile it by yourself)
 - Full-screen display

README_zh.md

@@ -163,6 +163,7 @@ Mac OS平台，你可以直接使用我编译好的可执行程序:
 - 实时显示Android设备屏幕
 - 实时键鼠控制Android设备
 - 屏幕录制
+- 截图为png
 - 无线连接
 - 最多支持16台设备连接（PC性能允许的情况下可以增加，需要自己编译）
 - 全屏显示