Add check to <static.md> #2

[skaunov]

Currently just making init() return None gives trivial solution.

[sunface]

I don't understand the meaning here, can you provide more context ?

[skaunov]

@sunface , the exercise asks not to change signature of init.

Make it work without changing the function signatures of init

So if the body of init replaced with the single word None the whole thing starts to work. So proposed added line is to hint reader that we don't mock him with a mind twister, and it really should be solved with lifetimes.