update README

README.md

@@ -37,15 +37,35 @@ It will compile a project for the `F4` family by default, but you can also compi
 # Usage
 
 First of all you need to configure toolchain and library paths using CMake variables. 
-You can do this by passing values through command line during cmake run or by setting variables
-inside your `CMakeLists.txt`. You can also pass these variables to CMake by setting them
-as environmental variables.
+You can do this by passing values through command line during cmake run with passed to CMake with 
+`-D<VAR_NAME>=...`or by setting variables inside your `CMakeLists.txt`. You can also pass these
+variables to CMake by setting them as environmental variables. The most important set of variables
+which needs to be set can be found in the following section
 
 ## Configuration
 
+These configuration options need to be  or by setting them 
+as environmental variables.
+
 * `STM32_TOOLCHAIN_PATH` - where toolchain is located, **default**: `/usr`
+* `STM32_CUBE_<FAMILY>_PATH` - path to STM32Cube directory, where `<FAMILY>` is one
+   of `F0 G0 L0 F1 L1 F2 F3 F4 G4 L4 F7 H7` **default**: `/opt/STM32Cube<FAMILY>`
+
+These configuration variables are optional:
+
 * `TARGET_TRIPLET` - toolchain target triplet, **default**: `arm-none-eabi`
-* `STM32_CUBE_<FAMILY>_PATH` - path to STM32Cube directory, where `<FAMILY>` is one of `F0 G0 L0 F1 L1 F2 F3 F4 G4 L4 F7 H7` **default**: `/opt/STM32Cube<FAMILY>`
+* `FREERTOS_PATH` - Path to the FreeRTOS kernel when compiling with a RTOS. Does not need to be
+   specified when using CMSIS
+
+Alternatively, you can write a small `path_helper.sh` script like this
+
+```sh
+export STM32_TOOLCHAIN_PATH=<ToolchainPath>
+export TARGET_TRIPLET=arm-none-eabi
+export STM32_CUBE_<FAMILY>_PATH=<PathToCubeRoot>
+```
+
+and then use `. path_helper.sh` to set up the environment in one go.
 
 ## Common usage