Add some missing question marks

src/linalg/cholesky.rs

@@ -119,7 +119,7 @@ where
 
     /// Returns the solution of the system `self * x = b` where `self` is the decomposed matrix and
     /// `x` the unknown.
-    #[must_use = "Did you mean to use solve_mut()"]
+    #[must_use = "Did you mean to use solve_mut()?"]
     pub fn solve<R2: Dim, C2: Dim, S2>(&self, b: &Matrix<T, R2, C2, S2>) -> OMatrix<T, R2, C2>
     where
         S2: Storage<T, R2, C2>,

src/linalg/qr.rs

@@ -164,7 +164,7 @@ where
     /// Solves the linear system `self * x = b`, where `x` is the unknown to be determined.
     ///
     /// Returns `None` if `self` is not invertible.
-    #[must_use = "Did you mean to use solve_mut()"]
+    #[must_use = "Did you mean to use solve_mut()?"]
     pub fn solve<R2: Dim, C2: Dim, S2>(
         &self,
         b: &Matrix<T, R2, C2, S2>,