Update 2024-01-25-lesson0.md

_posts/2024-01-25-lesson0.md

@@ -17,7 +17,7 @@ use std::env;        // (1) Imports `env` module. Compiler resolves this
                       //     to `std` library. No runtime cost directly.
 use std::fs::File;   // (2) Imports `File` struct. Compile-time symbol
                       //     resolution. `File` is an abstraction over OS
-                      //     file descriptors. System calls are the backend.
+                      //     file descriptors. System calls at  the backend.
 use std::io::{self, Read, Write}; // (3) Imports `io` module and traits. `self` brings
                                    //     module in scope. `Read`, `Write` traits are
                                    //     interfaces. Enables polymorphism via traits.