I have found instructions for 8 pin Tiny but none for my 20 pin. How do I set this chip up on the breadboard for bootloading with Arduino?
The principle is the same, it's all only ISP (In System Programming), and nothing different from any other microcontroller, that uses ISP. Look at the descriptions of the used pins for the 8-pin Attinys, then connect the pins with the same description on your 20-pin chip.
Namely you have to connect the pins MOSI, MISO, SCK, RESET, VCC and GND. MOSI and MISO are the data lines, SCK the clock signal. If you look into a pinout diagram or - even better - at the pin configuration diagram in the chips datasheet, you will see pins, that are marked this way. The rest of the pins is pretty much self explaining.
Since you are using an Uno as programmer and didn't have a capacitor between Reset and ground of the programmer, I will explain, why this capacitor is needed here.
The Atmega328p on the Uno doesn't have a native USB interface. So in order to connect it via USB to a PC, there is another microcontroller on the Uno (on original board the Atmega16U2), which has a native USB interface. This microcontroller then is the middleman between Atmega328P and PC. It connects to the Serial (UART) interface of the 328P and translates that to USB communication.
Everytime that the corresponding serial port is opened on the PC, the PC sends a DTR signal, which is connected to the 328P's reset pin. So, when the Arduino IDE tries to connect to the Serial port for flashing the Attiny, the Uno get's resetted and hence cannot flash the Attiny.
The capacitor between Reset and Ground will hold the Reset pin high for long enough, so that this reset does not happen and the Uno can do it's duty.
On Arduino boards with native USB interface this is not necessary, since they don't have this hardwired connection to a reset and they communicate directly over USB.