Add modifications from feedback

Author: romain-at-adacore

courses/rust_essentials/040_control_flow_basics/03_match.rst

@@ -20,12 +20,12 @@ Using "match" as a Statement
         0 => {
           println!("Grumble");
           println!("Must protest");
-        } // Comma is optional, unidiomatic
+        } // Comma is optional here, usually omitted
         1 => {
           println!("Tail wag engaged")
-        } // Block for single expression is optional, unidiomatic
-        2 => println!("Maximum happiness"),
-        _ => println!("Suspicion"), // Comma is optional, idiomatic
+        } // Block is valid but unnecessary for one line
+        2 => println!("Happiness!"), // Comma is REQUIRED here
+        _ => println!("Suspicion"),  // Trailing comma is allowed, idiomatic
     }
 
 --------------------------------

courses/rust_essentials/040_control_flow_basics/06_functions.rst

@@ -7,7 +7,7 @@ What is a function?
 ---------------------
 
 - Primary way to organize code into reusable blocks
-- Take inputs, process them, and (often) return a value
+- Take inputs, process them, and return a result (even if empty)
 - Declared using the :rust:`fn` keyword
   - Must be immediately followed by the body enclosed in :rust:`{ }` 
 - Typically in **snake_case** (e.g., :rust:`calculate_area`)