Schematic attached.
The double diode doesn't "help the bootloader". What it does is prevent the reset generator from interfering with the bootloader.
The reset generator helps prevent spurious PIC operation in the presence of "dirty" power, or start-up transient spikes. I once designed a PIC circuit that was powered by 110VAC. Everytime I switched on the power, the PIC would go "off in the weeds". This reset generator circuit solved the problem beautifully, and I've stuck with it ever since.
This particular reset generator imposes a 350mS delay upon power up and "other" power line disturbances, as well as debounces the reset switch. Note: there are other reset generators out there with shorter delays if 350mS is too long for your application.
When the bootloader "wiggles" the MCLR line, as part of it's normal start-up process, this would invoke a "fresh" (and undesirable) 350mS delay, from the reset generator, on the PIC reset pin if the double diode weren't there. Note: it doesn't have to be the BAT54 series diode, but it should be the Schottky type.
Newer PIC devices have brownout protection that may obviate this circuitry. I've just always used this circuit to solve a host of start-up and voltage transient problems.
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