Tweak to build instructions on includeos.github.io

[cratuki]

The website at includeos.org gives some instructions for getting started,

$ conan config install https://github.com/includeos/conan_config.git
$ git clone https://github.com/includeos/hello_world.git
$ mkdir build_hello_world
$ cd build_hello_world
$ conan install ../hello_world -pr  # * invalid usage
$ source ./activate.sh
$ cmake ../hello_world
$ cmake --build .
$ boot hello

These instructions do not work as written. One line above is marked.

Recommend fix: adapt the instructions from https://github.com/includeos/IncludeOS.

The instruction to run 'conan profile list' gives useful context, as do the recommending values for linux, etc.