rustdoc: wording for checkexec

Notably separating the summary line for correct display
at module level.

rust/hg-core/src/checkexec.rs

@@ -112,8 +112,10 b' fn check_exec_impl(path: impl AsRef<Path'
     Ok(false)
 }
 
-/// This function is a rust rewrite of `checkexec` function from `posix.py`
-/// Returns true if the filesystem supports execute permissions.
+/// This function is a Rust rewrite of the `checkexec` function from
+/// `posix.py`.
+///
+/// Returns `true` if the filesystem supports execute permissions.
 pub fn check_exec(path: impl AsRef<Path>) -> bool {
     check_exec_impl(path).unwrap_or(false)
 }