updated README.md file with tag reference and mdelay description

Signed-off-by: Armando Visconti <armando.visconti@st.com>

README.md

@@ -1,3 +1,5 @@
+![latest tag](https://img.shields.io/github/v/tag/STMicroelectronics/lsm6ds3tr-c-pid.svg?color=brightgreen)
+
 # 1 - Introduction
 
 Sensor driver for LSM6DS3TR-C sensor written in C programming language. This repository contains the sensor driver files (.h and .c) to be included, or linked directly as a git submodule, in your project. The driver is MISRA compliant and the documentation can be generated using the [Doxygen](http://www.doxygen.org/) tool.
@@ -16,8 +18,7 @@ Some examples of driver usage can be found [here](https://github.com/STMicroelec
 
 # 2 - Integration details
 
-The driver is platform-independent, you only need to define two  functions for read and write transactions from the sensor hardware bus  (ie. SPI or I²C). **A few devices integrate an extra bit in the  communication protocol in order to enable multi read/write access, this  bit must be managed in the read and write functions defined by the user.** Please refer to the read and write implementation in the [reference examples](https://github.com/STMicroelectronics/STMems_Standard_C_drivers/tree/master/lsm6ds3tr-c_STdC/examples).
-
+The driver is platform-independent, you only need to define two functions for read and write transactions from the sensor hardware bus (ie. SPI or I²C) and an optional one to implement a delay of millisecond granularity. **A few devices integrate an extra bit in the communication protocol in order to enable multi read/write access, this bit must be managed in the read and write functions defined by the user.** Please refer to the read and write implementation in the [reference examples](https://github.com/STMicroelectronics/STMems_Standard_C_drivers/tree/master/lsm6ds3tr-c_STdC/examples).
 
 
 ### 2.a Source code integration
@@ -27,8 +28,11 @@ The driver is platform-independent, you only need to define two  functions for r
 
 ```
 /** Please note that is MANDATORY: return 0 -> no Error.**/
-int32_t platform_write(void *handle, uint8_t Reg, const uint8_t *Bufp, uint16_t len)
-int32_t platform_read(void *handle, uint8_t Reg, uint8_t *Bufp, uint16_t len)
+int32_t platform_write(void *handle, uint8_t reg, const uint8_t *bufp, uint16_t len)
+int32_t platform_read(void *handle, uint8_t reg, uint8_t *bufp, uint16_t len)
+
+/** Optional (may be required by driver) **/
+void platform_delay(uint32_t millisec)
 ```
 
 - Declare and initialize the structure of the device interface:
@@ -37,6 +41,8 @@ int32_t platform_read(void *handle, uint8_t Reg, uint8_t *Bufp, uint16_t len)
 xxxxxxx_ctx_t dev_ctx; /** xxxxxxx is the used part number **/
 dev_ctx.write_reg = platform_write;
 dev_ctx.read_reg = platform_read;
+dev_ctx.mdelay = platform_delay;
+
 ```
 
 - If needed by the platform read and write functions, initialize the handle parameter: