Add under troubleshooting section how to install latest npm

[crtahlin]

In case of Ubuntu 22.04, just using npm installation procedure as in readme file will result in swarm-cli not working.

Instead, this procedure could be followed for successful swarm-cli installation:

    apt install npm
    npm install --global @ethersphere/swarm-cli
    sudo npm cache clean -f
    sudo npm install -g n
    sudo n stable
    node -v
    swarm-cli

(Above works on my system(s), TM.)