Fixed some documentation in the v2 mb readme

Author: r59q

microbit/v2/.gitignore

@@ -16,4 +16,6 @@ buildcache.json
 *.pyc
 
 build_and_move.sh
-build_clear_and_move.sh
+build_clear_and_move.sh
+
+samples/

microbit/v2/README.md

@@ -14,17 +14,24 @@ You need some open source pre-requisites to build this repo. You can either inst
 - [Github desktop](https://desktop.github.com/)
 - [CMake](https://cmake.org/download/)
 - [Python 3](https://www.python.org/downloads/)
+- For OS X you may need command line tools for xcode. Install using `xcode-select --install`
 
 **OR**
 
 One can use docker instead of downloading these dependencies (read about this here [here](https://github.com/lancaster-university/microbit-v2-samples))
 
 # Building without docker
 - Clone this repository
-- In the root of this repository type `python3 build.py` or `python build.py` depending on python version
-- The hex file will be built `MICROBIT.HEX` and placed in the root folder.
+- In the folder `/microbit/v2` type `execute python3 build.py` or `python build.py` depending on python version
+- The hex file will be built `MICROBIT.HEX` and placed in the `/microbit/v2` folder.
 - If at some point any config changes are made outside any .cpp files run `python3 build.py -c`. The `-c` flag will clear the build files. If this is not done the changes to config will not take effect.
 
+**Note**: for OS X users receiving the error 
+
+```xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun```
+
+install xcode command line tools using `xcode-select --install`
+
 ### Broken .hex fix
 If at some point the HEX file doesn't seem to work, but compiles fine, check `codal.json` to see if the following is missing.