fix some spelling

Author: zingale

docs/source/adding_a_problem_jupyter.ipynb

@@ -114,7 +114,7 @@
    "id": "6f682998-c452-4fdf-87dc-bac340e9e9df",
    "metadata": {},
    "source": [
-    "It often works best if you start with an existing problem.  We can inspect the source of one of the build-in problems easily:"
+    "It often works best if you start with an existing problem.  We can inspect the source of one of the built-in problems easily:"
    ]
   },
   {

docs/source/rt_average.ipynb

@@ -13,7 +13,7 @@
    "id": "6395d3eb-9572-454b-823a-b5c2f8c4267d",
    "metadata": {},
    "source": [
-    "Here we show how to do a lateral / horizonal average of the compressible Rayleigh-Taylor\n",
+    "Here we show how to do a lateral / horizontal average of the compressible Rayleigh-Taylor\n",
     "simulation to see what the average vertical profile of the mixing looks like."
    ]
   },