heading fix for rotation broadening notebook

docs/rotation_broadening/rotation_broadening.ipynb

@@ -92,7 +92,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### STARDIS contains a post-simulation function to broaden the spectrum appropriate for a v sin(i) given by the user. However, this is only physically valid when the spectrum broadened is given over a small range of frequencies or wavelengths, or is constant in velocity resolution across the spectrum. \n",
+    "STARDIS contains a post-simulation function to broaden the spectrum appropriate for a v sin(i) given by the user. However, this is only physically valid when the spectrum broadened is given over a small range of frequencies or wavelengths, or is constant in velocity resolution across the spectrum. \n",
     "\n",
     "First, let's run a small, simple STARDIS simulation with a spectral resolution $R \\sim 100000$"
    ]