docs(troubleshooting): Mention the ESP Hardware Design Guidelines docs

.github/ISSUE_TEMPLATE/issue-with-hw.yml

@@ -7,7 +7,7 @@ body:
       value: |
         * Most failures to connect, flash, etc. are problems with the hardware.
         * Please check any guide that came with your hardware, and also check [the esptool troubleshooting guide](https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html).
-        * If your board is a custom design, consider using our [free-of-charge schematic and PCB review service](https://www.espressif.com/en/contact-us/circuit-schematic-pcb-design-review).
+        * If your board is a custom design, check the [ESP Hardware Design Guidelines](https://docs.espressif.com/projects/esp-hardware-design-guidelines/) and consider using our [free-of-charge schematic and PCB review service](https://www.espressif.com/en/contact-us/circuit-schematic-pcb-design-review).
         * If still experiencing the issue, please provide as many details as possible below about your hardware and computer setup.
   - type: input
     id: os

docs/en/troubleshooting.rst

@@ -5,7 +5,9 @@
 Troubleshooting
 ===============
 
-Flashing problems can be fiddly to troubleshoot. Try the suggestions here if you're having problems:
+Flashing problems can be fiddly to troubleshoot. The underlying issue can be caused by the drivers, OS, hardware, or even a combination of these. If your board is a custom design, check the `ESP Hardware Design Guidelines <https://docs.espressif.com/projects/esp-hardware-design-guidelines/>`_ or consider using our `free-of-charge schematic and PCB review service <https://www.espressif.com/en/contact-us/circuit-schematic-pcb-design-review>`_.
+
+Try the following suggestions if your issues persist:
 
 Bootloader Won't Respond
 ------------------------