Minor adjustments to text

docs/tutorials/creating-a-landsat-stac.ipynb

@@ -133,7 +133,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We can then use these classes to get the MTL file for our scene. Notice we use pystac.STAC_IO.read_text - this is the method that PySTAC uses to read text as it crawls a STAC. It can read from the local filesystem or HTTP/HTTPS by default. Also, it can be extended to read from other sources such as cloud providers—[see the documentation here](https://pystac.readthedocs.io/en/latest/concepts.html#using-stac-io). For now we'll use it directly as an easy way to read a text file from an HTTPS source."
+    "We can then use these classes to get the MTL file for our scene. Notice we use `pystac.STAC_IO.read_text`; this is the method that PySTAC uses to read text as it crawls a STAC. It can read from the local filesystem or HTTP/HTTPS by default. Also, it can be extended to read from other sources such as cloud providers—[see the documentation here](https://pystac.readthedocs.io/en/latest/concepts.html#using-stac-io). For now we'll use it directly as an easy way to read a text file from an HTTPS source."
    ]
   },
   {
@@ -609,7 +609,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We can see we'll need at least an `id`, `geometry`, `bbox`, and `datetime`. Properties is required, but can be an empty dictionary that we fill out on the Item once it's created."
+    "We can see we'll need at least an `id`, `geometry`, `bbox`, and `datetime`. Properties is required, but can be an empty dictionary that we fill out on the Item once it's created.\n",
+    "\n",
+    "> Caution! The `Optional` type hint is used when None can be provided in place of a meaningful argument; it does not indicate that the argument does not need to be supplied—that is only true if a default value is indicated in the type signature."
    ]
   },
   {