Use environment variable instead of /<source_root>/ to simplify the instruction following

[aosadchyy]

Currently instructions need to be modified from <source_root> to a specific location. e.g.
cd /<source_root>/ => cd /src/

To enable a simple copy & paste of the build instructions in the docs. Suggest to use an environment variable for the <source_root>. e.g.
export SOURCE_ROOT=/src
cd $SOURCE_ROOT
export PATH=$PATH;$SOURCE_ROOT/bin
...