Add warning regarding different struct layouts on Apple M1

[MoritzKn]

As discussed in #210

[c0gent]

Let's see what you determine is the best solution for your issue based on my latest comment in #210 then we can update this with some documentation for future users encountering the same problem.

[MoritzKn]

My understanding was that repr “C would create C ABI compatible structs (and other data types). Hence I interpreted the comment/documentation on OclPrm as allowing structs to be OclPrm as long as they have repr “C. If that's not the case I'd simply clarify that statement. What data types does the statement still apply to? Single fields structs? Unions?

[c0gent]

Ok I'll leave this open until I can come up with more clarifying documentation at some point.