Chapter II
"...I do not allow friendly association with other people, nor do I deprive them that are my own and that obey me of anything that is good for them."
It depends on what kind of christian they are, basically it comes down to how deep they practice their Christianity.
To me, if they are christian for just names due to their birth in a christian family and hardly practice any christianity, then the friendship is possible but also depends on their behavior. And if someone is deep into Christianity, I just try to keep a distance and don't bother with them. And if such hardcore christians engage with me to try to form a friendship, I try not to engage with them and after a while they always lose interest in me on their own.
Also, don't or try not to take favours you cannot return if you ever become friends with a christian or muslim. This is a general advice for any kind of relationship, though.