Update index.md

Author: Prashant-Shekhar-Rao

src/mir/index.md

@@ -62,7 +62,9 @@ show you the MIR for your program. Try putting this program into play
 button on the top:
 
 [sample-play]: https://play.rust-lang.org/?gist=30074856e62e74e91f06abd19bd72ece&version=stable
-MIR shown by link is missing some statements for unoptimized MIR use `-Z mir-opt-level=0 --emit mir`
+MIR shown by above link is optimized. The compiler removes some statements in optimization like `StorageLive`. This happens because compiler notices the value is never acessed in the code. We can use `rustc [filename].rs -Z mir-opt-level=0 --emit mir` to view unoptimized MIR. This requires nightly toolchain.
+
+```
 ```rust
 fn main() {
     let mut vec = Vec::new();