Minor build-it.md changes

Explain as provided build command and Cargo.toml file will handle turning off optimizations and improve the verbiage about this build doesn't blink the lights.

Author: DaQue

src/05-led-roulette/build-it.md

@@ -45,9 +45,9 @@ $ cargo build --target thumbv7em-none-eabihf
     Finished dev [unoptimized + debuginfo] target(s) in 35.84 secs
 ```
 
-> **NOTE** Be sure to compile this crate *without* optimizations
+> **NOTE** Be sure to compile this crate *without* optimizations. The provided Cargo.toml file used with the build command givn above will ensure optimizations are off. Just don't add any extra build options.
 
-OK, now we have produced an executable. This isn't a version that will actually blink any leds but a simplified version we will build on through the rest of the chapter. As a sanity check, let's verify that the produced executable is actually an ARM binary:
+ OK, now we have produced an executable. This executable won't blink any leds, it's just a simplified version that we will build upon through out the rest of the chapter. As a sanity check, let's verify that the produced executable is actually an ARM binary:
 
 ``` console
 $ # equivalent to `readelf -h target/thumbv7em-none-eabihf/debug/led-roulette`