Update fourier.ipynb

Author: pavelkomarov

notebooks/fourier.ipynb

@@ -7,7 +7,7 @@
    "source": [
     "# Fourier Usage Examples\n",
     "\n",
-    "This notebook shows off some of what the `fourier_deriv` function can do. Note the set of mathematical functions that can work with this method is much more constrained than that `cheb_deriv` can handle. Much of this notebook is dedicated to showing how `fourier_deriv` can fail. But if you have periodic boundary conditions or [can "extend" your function to be periodic](https://github.com/pavelkomarov/spectral-derivatives/blob/main/notebooks/fourier_periodic_extensions.ipynb), then you may prefer this."
+    "This notebook shows off some of what the `fourier_deriv` function can do. Note the set of mathematical functions that can work with this method is much more constrained than that `cheb_deriv` can handle. Much of this notebook is dedicated to showing how `fourier_deriv` can fail. But if you have periodic boundary conditions or [can \"extend\" your function to be periodic](https://github.com/pavelkomarov/spectral-derivatives/blob/main/notebooks/fourier_periodic_extensions.ipynb), then you may prefer this."
    ]
   },
   {