Merge pull request #1802 from AndreasHuber/AndreasHuber-patch-1

fix(str.md): avoid misunderstanding that there were only two string types

src/std/str.md

@@ -1,6 +1,6 @@
 # Strings
 
-There are two types of strings in Rust: `String` and `&str`.
+The two most used string types in Rust are `String` and `&str`.
 
 A `String` is stored as a vector of bytes (`Vec<u8>`), but guaranteed to
 always be a valid UTF-8 sequence. `String` is heap allocated, growable and not