screencapture: add page (#3390)

pages/osx/screencapture.md

@@ -0,0 +1,27 @@
+# screencapture
+
+> Utility to take screenshots and screen recordings.
+
+- Take a screenshot and save it to a file:
+
+`screencapture {{path/to/file.png}}`
+
+- Take a screenshot including the mouse cursor:
+
+`screencapture -C {{path/to/file.png}}`
+
+- Take a screenshot and open it in Preview, instead of saving:
+
+`screencapture -P`
+
+- Take a screenshot of a selected rectangular area:
+
+`screencapture -i {{path/to/file.png}}`
+
+- Take a screenshot after a delay:
+
+`screencapture -T {{seconds}} {{path/to/file.png}}`
+
+- Make a screen recording and save it to a file:
+
+`screencapture -v {{path/to/file.mp4}}`