Update README.md

Author: pdp7

README.md

@@ -7,8 +7,8 @@
 Adafruit BBIO is an API to enable [GPIO](README.md#gpio-setup), [PWM](README.md#pwm), [ADC](README.md#adc), [UART](README.md#uart), [SPI](README.md#spi) and [eQEP](README.md#eqep) (Quadrature Encoder) hardware access from Python applications running on the Beaglebone. 
 
 * It is recommended to use an [official BeagleBoard.org Debian image](https://beagleboard.org/latest-images)
-  * **Currently recommended image: [Debian 9.4 "Stretch" IoT (2018-06-17)](http://debian.beagleboard.org/images/bone-debian-9.4-iot-armhf-2018-06-17-4gb.img.xz)**
-    * Install [Linux kernel](https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Kernel_Options) [4.14.x](https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Mainline_.284.14.x_lts.29) to enable [non-root control of GPIO](https://github.com/rcn-ee/repos/blob/master/bb-customizations/suite/stretch/debian/80-gpio-noroot.rules) and [PWM](https://github.com/rcn-ee/repos/blob/master/bb-customizations/suite/stretch/debian/81-pwm-noroot.rules) [_(commit)_](https://github.com/adafruit/adafruit-beaglebone-io-python/commit/b65cbf8e41b444bad7c4ef6cfd4f88a30210fd78)
+  * **Currently recommended image: [Debian 9.9 "Stretch" IoT (2019-08-03)](https://debian.beagleboard.org/images/am57xx-debian-9.9-lxqt-armhf-2019-08-03-4gb.img.xz)**
+    * Install [Linux kernel](https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Kernel_Options) [4.14.x](https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Mainline_.284.14.x_lts.29), or newer, to enable [non-root control of GPIO](https://github.com/rcn-ee/repos/blob/master/bb-customizations/suite/stretch/debian/80-gpio-noroot.rules) and [PWM](https://github.com/rcn-ee/repos/blob/master/bb-customizations/suite/stretch/debian/81-pwm-noroot.rules) [_(commit)_](https://github.com/adafruit/adafruit-beaglebone-io-python/commit/b65cbf8e41b444bad7c4ef6cfd4f88a30210fd78)
 
 * Adafruit_BBIO supports Linux kernels 3.8 through 4.14