Update the Speaker Notes of the type-inference.md (#214)

* Update the Speaker Notes of the type-inference.md

I think this is one of the critical moments in understanding Rust. This behavior is different from many static and dynamic programming languages.

* Fix typo

Co-authored-by: Andrew Walbran <[email protected]>

Author: igor-petruk

src/basic-syntax/type-inference.md

@@ -24,6 +24,10 @@ fn main() {
 <details>
 
 This slide demonstrates how the Rust compiler infers types based on constraints given by variable declarations and usages.
+    
+It is very important to emphasize that variables declared like this are not of some sort of dynamic "any type" that can
+hold any data. The machine code generated by such declaration is identical to the explicit declaration of a type.
+The compiler does the job for us and helps us to write a more concise code.
 
 The following code tells the compiler to copy into a certain generic container without the code ever explicitly specifying the contained type, using `_` as a placeholder: