backend: Fix a bug where pump stops when focus is over (#597)

I saw this by chance in the code. I couldn't find an open isssue in
https://github.com/PlanktoScope/PlanktoScope but @chevreuill3000 did
mention it in the past.

Author: sonnyp

device-backend/control/planktoscopehat/planktoscope/stepper.py

@@ -443,7 +443,7 @@ def run(self):
                     '{"status":"Done"}',
                 )
                 self.focus_started = False
-                self.pump_stepper.release()
+                self.focus_stepper.release()
             time.sleep(0.01)
         logger.info("Shutting down the stepper process")
         self.actuator_client.client.publish("status/pump", '{"status":"Dead"}')

documentation/docs/community/contribute/tips-and-tricks.md

@@ -142,7 +142,7 @@ sudo dd bs=1M if=/dev/device status=progress conv=fdatasync | xz > sdcard.img.xz
 
 ```sh
 # restore an image file from your computer onto the SD card
-xzcat sdcard.img.xz | sudo dd bs=1M of=/dev/device status=progress
+xzcat sdcard.img.xz | sudo dd bs=1M of=/dev/device status=progress conv=fdatasync
 ```
 
 See also the operating guide [SD Card Cloning](../../operation/clone-sd.md).