solutions link point to github repo instead of actual github page

[Akhil]

It's very painful to navigate to right page under solutions folder.

In char-bool-unit page the solution link points to https://github.com/sunface/rust-by-practice instead of https://github.com/sunface/rust-by-practice/blob/master/solutions/basic-types/char-bool.md

Solutions link in char-bool-unit page:

You can find the solutions here(under the solutions path), but only use it when you need it

It would be great if we have solutions link pointing to actual page.