readme: fix link to esp32 port

Author: mringwal

README.md

@@ -42,7 +42,7 @@ GATT, SM of the Bluetooth 4.2 LE Central and Peripheral roles (QD ID 25340). For
 
 Build Status               | Port | Platform
 ---------------------| -----| ------
-[<img src="http://buildbot.bluekitchen-gmbh.com/btstack/badge.png?builder=port-esp32-master">](https://buildbot.bluekitchen-gmbh.com/btstack/builders/port-esp32-master) | [Espressif ESP32](http://www.espressif.com/products/hardware/esp32/overview) 2.4 GHz Wi-Fi and Bluetooth Dual-Mode combo chip using [FreeRTOS](http://www.freertos.org)
+[<img src="http://buildbot.bluekitchen-gmbh.com/btstack/badge.png?builder=port-esp32-master">](https://buildbot.bluekitchen-gmbh.com/btstack/builders/port-esp32-master) | [esp32](https://github.com/bluekitchen/btstack/tree/master/port/esp32) | [Espressif ESP32](http://www.espressif.com/products/hardware/esp32/overview) 2.4 GHz Wi-Fi and Bluetooth Dual-Mode combo chip using [FreeRTOS](http://www.freertos.org)
 [<img src="http://buildbot.bluekitchen-gmbh.com/btstack/badge.png?builder=port-ez430-rf2560-master">](https://buildbot.bluekitchen-gmbh.com/btstack/builders/port-ez430-rf2560-master) | [ez430-rf2560](https://github.com/bluekitchen/btstack/tree/master/port/ez430-rf2560) | [EZ430-RF256x Bluetooth Evaluation Tool for MSP430](http://www.ti.com/tool/ez430-rf256x)
 [<img src="http://buildbot.bluekitchen-gmbh.com/btstack/badge.png?builder=port-msp-exp430f5438-cc2564b-master">](https://buildbot.bluekitchen-gmbh.com/btstack/builders/port-msp-exp430f5438-cc2564b-master) | [msp-exp430f5438-cc2564b](https://github.com/bluekitchen/btstack/tree/master/port/msp-exp430f5438-cc2564b) |[MSP430F5438 Experimenter Board for MSP430](http://www.ti.com/tool/msp-exp430f5438) with [Bluetooth CC2564 Module Evaluation Board](http://www.ti.com/tool/cc2564modnem)
 [<img src="http://buildbot.bluekitchen-gmbh.com/btstack/badge.png?builder=port-msp430f5229lp-cc2564b-master">](https://buildbot.bluekitchen-gmbh.com/btstack/builders/port-msp430f5229lp-cc2564b-master)     | [msp430f5529lp-cc2564b](https://github.com/bluekitchen/btstack/tree/master/port/msp430f5229lp-cc2564b) | [MSP-EXP430F5529LP LaunchPad](http://www.ti.com/ww/en/launchpad/launchpads-msp430-msp-exp430f5529lp.html#tabs) with [Bluetooth CC2564 Module Evaluation Board](http://www.ti.com/tool/cc2564modnem) and [EM Adapter BoosterPack](http://www.ti.com/tool/boost-ccemadapter) with additional 32768Hz quartz oscillator