docs: copy line to other one

Author: prestwich

src/utils/from_env.rs

@@ -379,6 +379,9 @@ pub trait FromEnvVar: core::fmt::Debug + Sized + 'static {
     /// Load the primitive from the environment at the given variable. If the
     /// variable is unset or empty, return the value generated by
     /// [`Default::default`].
+    ///
+    /// This function will return an error if the environment variable is set
+    /// but cannot be parsed.
     fn from_env_var_or_default(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>
     where
         Self: Default,