Fix typo correction ("then" -> "then the")

Author: krepl

src/c-tips/index.md

@@ -62,7 +62,7 @@ full details of the conditional compilation support, refer to the
 [conditional compilation]: https://doc.rust-lang.org/reference/conditional-compilation.html
 
 The conditional compilation will only apply to the next statement or block. If
-a block can not be used in the current scope then `cfg` attribute will
+a block can not be used in the current scope then the `cfg` attribute will
 need to be used multiple times.  It's worth noting that most of the time it is
 better to simply include all the code and allow the compiler to remove dead
 code when optimising: it's simpler for you and your users, and in general the