Fix image links in README.md.

browser/README.md

@@ -4,7 +4,7 @@ This is an example web browser built with Python and Qt. Using the
 QtWebEngineWidgets system introduced in Qt5.6, this provides a single-window
 browsing experience with the usual controls, as well as saving and loading HTML.
 
-![Browser](screenshot-browser.png)
+![Browser](screenshot-browser.jpg)
 
 > If you think this example app is neat and want to learn more about
 PyQt in general, [take a look at my ebook & online course

browser_tabbed/README.md

@@ -5,7 +5,7 @@ browsing! Go back and forward! Print! Save files! Get help!
 (you’ll need it). Any similarity to other browsers is entirely 
 coincidental.
 
-![Browser tabbed](screenshot-browser-tabbed.png)
+![Browser tabbed](screenshot-browser-tabbed.jpg)
 
 > If you think this example app is neat and want to learn more about
 PyQt in general, [take a look at my ebook & online course

weather/README.md

@@ -3,7 +3,7 @@
 Get your daily weather and 15hr forecast. Data is provided by the free
 weather and forecast API from https://openweathermap.org/
 
-![Weather](screenshot-weather.png)
+![Weather](screenshot-weather.jpg)
 
 > If you think this example app is neat and want to learn more about
 PyQt in general, [take a look at my ebook & online course