tests.nixpkgs-check-by-name: Minor doc updates

pkgs/test/nixpkgs-check-by-name/README.md

@@ -1,6 +1,6 @@
 # Nixpkgs pkgs/by-name checker
 
-This directory implements a program to check the [validity](#validity-checks) of the `pkgs/by-name` Nixpkgs directory once introduced.
+This directory implements a program to check the [validity](#validity-checks) of the `pkgs/by-name` Nixpkgs directory.
 It is being used by [this GitHub Actions workflow](../../../.github/workflows/check-by-name.yml).
 This is part of the implementation of [RFC 140](https://github.com/NixOS/rfcs/pull/140).
 
@@ -24,7 +24,7 @@ This API may be changed over time if the CI workflow making use of it is adjuste
   - `2`: If an unexpected I/O error occurs
 - Standard error:
   - Informative messages
-  - Error messages if validation is not successful
+  - Detected problems if validation is not successful
 
 ## Validity checks
 

pkgs/test/nixpkgs-check-by-name/src/main.rs

@@ -68,8 +68,8 @@ fn main() -> ExitCode {
 ///
 /// # Return value
 /// - `Err(e)` if an I/O-related error `e` occurred.
-/// - `Ok(false)` if the structure is invalid, all the structural errors have been written to `error_writer`.
-/// - `Ok(true)` if the structure is valid, nothing will have been written to `error_writer`.
+/// - `Ok(false)` if there are problems, all of which will be written to `error_writer`.
+/// - `Ok(true)` if there are no problems
 pub fn check_nixpkgs<W: io::Write>(
     nixpkgs_path: &Path,
     version: Version,