fix lab2 pico img

book/labs/2_determine_heart_rate/lab2.ipynb

@@ -263,7 +263,7 @@
     "First, ask your TA for today's hardware and pull out your pico. Find the BOOTSEL button (see the below diagram), press and hold it down, and then plug in your pico while continuing to hold the button. After 5 seconds, you can let go of the button. Next, [click this link](https://micropython.org/resources/firmware/RPI_PICO-20220618-v1.19.1.uf2) to download the Micropython firmware. Navigate to your downloads folder, and find the `.uf2` file that was just downloaded and drag it into the pico folder, which can be found on the left side panel called `/RPI-RP2`. After a second or two, the pico should reboot, and the `/RPI-RP2` folder will go away. After a few more seconds, open up thonny, and press the button in the bottom right, which may say something like \"Python 3.x.x\", \"Micropython\", or \"Select interpreter\". A pop up window should come up, in that window select `Micropython`, then press done. The terminal in thonny will probably have an error at this point, if so just rapidly click the Stop/Restart button in the top bar, which looks like a red stop sign. If the red message doesn't go away after about 30 seconds of clicking, double check you followed the steps correctly, then ask your TA if the problem persists.\n",
     "\n",
     "<div>\n",
-    "<img src=\"pico_bootsel.png\" alt=\"bootsel button diagram\" width=\"400\"/>\n",
+    "<img src=\"https://raw.githubusercontent.com/TheDataScienceLabs/DSLab_Calculus/main/book/labs/2_determine_heart_rate/pico_bootsel.png\" alt=\"bootsel button diagram\" width=\"400\"/>\n",
     "</div>\n",
     "\n",
     "\n",