Update hrit_msg_tutorial.ipynb

Based on the thread at pytroll/satpy#1517, this is a better example to avoid importing two timesteps onto a scene, and adds clarification about the warnings which are expected but would throw off a new user.

satpy/hrit_msg_tutorial.ipynb

@@ -32,19 +32,21 @@
     "from satpy.resample import get_area_def\n",
     "from satpy import find_files_and_readers\n",
     "from datetime import datetime\n",
+    "import glob\n",
+    "import warnings\n",
     "\n",
-    "files = find_files_and_readers(base_dir='../hrit_seviri/test_data', \n",
-    "                               start_time=datetime(2017, 1, 19, 9, 30),\n",
-    "                               end_time=datetime(2017, 1, 19, 9, 45),\n",
-    "                               reader='seviri_l1b_hrit')\n",
-    "scn = Scene(filenames=files)"
+    "# Date format in YYYYMMDDhhmm\n",
+    "fnames = glob.glob("/path/to/data/H*202009060000*__")\n",
+    "scn = Scene(reader="seviri_l1b_hrit", filenames=fnames)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We then define a composite to load and show it:"
+    "We then define a composite to load and show it.\n",
+    "Several warnings will occur related to pyproj deprecating the use of ‘PROJ Strings’ and also numpy/dask due to the use of NaNs for invalid pixels including space pixels (like you'll see in a full disk image). To hide these, use:\n",
+    "warnings.filterwarnings('ignore')"
    ]
   },
   {