Edits to READMEs. Removed video that was not playing properly

examples/adc_polled/README.md

@@ -7,3 +7,8 @@ busy-waits until the conversion is complete before reading the result.
 This is just about the simplest and easiest use-case for the ADC and wastes a lot
 of CPU cycles but it does show the basics of doing conversions in a situation
 where high performance is not needed.
+
+## Use
+Connect an analog voltage source that varies between 0V and 3.3v to GPIO pin PD4
+and a 3.3V logic level serial terminal to pin PD5. The 10-bit result will be
+printed periodically on the serial output.

examples/i2c_oled/README.md

@@ -6,8 +6,6 @@ pixels, lines, circles, rectangles and 8x8 character font rendering. Out of the
 box this demo cycles through a few different graphic screens to test out the
 various drawing primitives.
 
-[OLED video](doc/oled.mp4)
-
 ## Use
 Connect an SSD1306-based OLED in I2C interface mode to pins PC1 (SCL) and PC2 (SDA)
 of the CH32V003 with proper I2C pullup resistors and observe the various graphic

examples/systick_irq/README.md

@@ -13,4 +13,10 @@ for IRQs.
 Note also the use of the  `__attribute__((interrupt))` syntax in declaring the
 IRQ handler. Some of the IRQ examples from the WCH HAL library have slightly
 different syntax to make use of a fast IRQ mode but which is not compatible with
-generic RISC-V GCC so that feature is not used here.
\ No newline at end of file
+generic RISC-V GCC so that feature is not used here.
+
+# Use
+Connect LEDs (with proper current limit resistors) to GPIO pins C0, D0, D4 and
+a 3.3V logic level serial terminal to PD5. The LEDs will flash and an incrementing
+count will be printed to the serial port at rates that are controlled by the
+Systick IRQ.