redo the section readmes

exercises/if/README.md

@@ -0,0 +1,7 @@
+### If
+
+`if`, the most basic type of control flow, is what you'll learn here.
+
+#### Book Sections
+
+- [Control Flow - if expressions](https://doc.rust-lang.org/stable/book/ch03-05-control-flow.html#if-expressions)

exercises/if/REAMDE.md

@@ -1 +0,0 @@
-For this exercise check out the chapter [If](https://doc.rust-lang.org/book/2018-edition/ch03-05-control-flow.html?highlight=control,fl#control-flow) of the Rust Book.