Chapter 12.4 uses a backslash within a string without explaining what it does #2597

Listing 12-15 in chapter 12.4 includes the definition of a string:

    let contents = "\
Rust:
safe, fast, productive.
Pick three.";

The use of the backslash on the first line of this definition is not explained, and I don't believe it is covered in the previous chapters. It would be useful to have a short explanation of its purpose.

https://doc.rust-lang.org/reference/tokens.html has this explanation:

... as a special exception, when an unescaped U+005C character (\) occurs immediately before the line-break, then the U+005C character, the line-break, and all whitespace at the beginning of the next line are ignored.

I suggest adding wording similar to the following in the first paragraph after listing 12-15:

The backslash at the end of the first line of contents prevents Rust including a blank line at the beginning of the string.