Add more notes about general usage.

ch32v003fun/ch32v003fun.h

@@ -28,13 +28,23 @@
  5. printf
  printf, _write may be semihosted, or printed to UART.
 
- poll_input, handle_debug_input may be used with semihsoting.
+ poll_input, handle_debug_input may be used with semihsoting to accept input from host.
 
- For UART printf, on:
- CH32V003, Port D5, 115200 8n1
- CH32V203, Port A9, 115200 8n1
+  For UART printf, on:
+  CH32V003, Port D5, 115200 8n1
+  CH32V203, Port A9, 115200 8n1
 
- Modifications can be made to SetupUart, or your own version as desired.
+ Modifications can be made to SetupUart, or your own version as desired.
+
+ 6. ISR Control Routines
+ __enable_irq(); // For global interrupt enable
+ __disable_irq(); // For global interrupt disable
+ __isenabled_irq(); // For seeing if interrupts are enabled.
+ NVIC_EnableIRQ(IRQn_Type IRQn) // To enable a specific interrupt
+
+ 7. Hardware MMIO structs, i.e.
+ SysTick->CNT = current system tick counter (can be Hclk or Hclk/8)
+ TIM2->CH1CVR = direct control over a PWM output
 */