Add type inference example

[phansch]

This should make the chapter a bit more approachable, as it doesn't
start out with a reference to the HM type inference algorithm.

[alexcameron89]

As someone currently reading through the guide, I appreciate this addition.

I am curious, is there a reason for using inferenced over inferred? I thought that the latter was correct.

[phansch]

Thanks! I'm doing the same right now to potentially fix rust-lang/rust#50548 at some point in the future :)

As for inferenced vs inferred, I'm not a native English speaker and inferenced seems to be used everywhere else in the guide.(Actually no)
There's some discussion on english.stackexchange.org which suggests that inferencing is used in linguistics, which could apply here as well, I guess. But I'm open to change it to inferred/inferring 👍

[alexcameron89]

Oh very interesting, thanks for sharing!

[mark-i-m]

Thanks!

Just a minor nit, then r=me.

Re: inferred vs inferenced: I think we can leave this as-is for now. If someone else comes along with more info later, we can revisit...

[mark-i-m]

Nit: "things is inferenced to be &str" -> "the type of things is ..."

[phansch]

Fixed 👍

[mark-i-m]

Thanks!