Update cheatsheets

tldr/qr

@@ -10,8 +10,16 @@ source: https://github.com/tldr-pages/tldr.git
 
 - Generate a QR code:
 
-`echo "{{data}}" | qr`
+`qr "{{data}}"`
 
-- Specify the error correction level (defaults to M):
+- Specify the error correction level (defaults to `M`):
 
-`echo "{{data}}" | qr --error-correction={{L|M|Q|H}}`
+`qr --error-correction {{L|M|Q|H}} "{{data}}"`
+
+- Generate a QR code from the output of another command:
+
+`{{command}} | qr`
+
+- Save the QR code as a PNG image:
+
+`qr "{{data}}" > {{path/to/file.png}}`