Add explanation for influence of atmospheric conditiosn (#113)

Author: AdamRJensen

docs/source/refraction_introduction.ipynb

@@ -166,7 +166,7 @@
    "source": [
     "## Influence of atmospheric conditions\n",
     "\n",
-    "Some refraction models are able to account for the influence of temperature and pressure. Noticeably, the inputs are annual averages, and thus, time series should not be provided.\n",
+    "Some refraction models are able to account for the influence of temperature and pressure, which affects density and thus atmospheric refraction. Existing algorithms were derived based on annual averages, and thus, time series should not be provided.\n",
     "\n",
     "Looking at the plots below, it is evident that a higher annual average temperature decreases refraction. On the contrary, a higher annual average pressure increases refraction.\n",
     "\n",