add section heading to template string docs

Author: mscarey

docs/guides/template_strings.rst

@@ -129,6 +129,12 @@ Comparison object must end with the word “was”. AuthoritySpoke will then
 build the rest of the phrase using the comparison sign and expression
 that you provide.
 
+Comparisons with Measurements and Units
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To use a measurement as a Comparison’s ``expression``, pass the measurement as
+a string when constructing the Comparison object, and it will be converted to a :class:`pint.Quantity`\.
+
     >>> from authorityspoke import Comparison
     >>> drug_comparison = Comparison(
     >>>     "the weight of marijuana that $defendant possessed was",
@@ -183,6 +189,10 @@ asserted the weight was much greater.
     >>> drug_comparison_with_upper_bound.contradicts(drug_comparison)
     True
 
+The unit that the Comparison parses doesn't have to be weight. It could also be distance, time, volume,
+units of surface area such as square kilometers or acres, or units that combine multiple dimensions
+such as miles per hour or meters per second.
+
 Comparisons with Integer and Float Expressions
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

notebooks/template_strings_and_explanations.ipynb

@@ -209,6 +209,20 @@
     "AuthoritySpoke's `Comparison` class extends the concept of a `Predicate`. A `Comparison` still contains a `truth` value and a `template` string, but that template should be used to identify a quantity that will be compared to an `expression` using a `sign` such as an equal sign or a greater-than sign. This `expression` must be a constant: either an integer, a floating point number, a date, or a physical quantity expressed in units that can be parsed using the [pint library](https://pint.readthedocs.io/en/stable/defining-quantities.html#using-string-parsing). To encourage consistent phrasing, the template string in every Comparison object must end with the word \"was\". AuthoritySpoke will then build the rest of the phrase using the comparison sign and expression that you provide."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Comparisons with Measurements and Units"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "To use a measurement as a Comparison's `expression`, pass the measurement as a string when constructing the Comparison object, and it will be converted to a `pint` object."
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 8,
@@ -364,6 +378,15 @@
     "drug_comparison_with_upper_bound.contradicts(drug_comparison)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "The unit that the Comparison parses doesn't have to be weight. It could also be distance, time, volume,\n",
+    "units of surface area such as square kilometers or acres, or units that combine multiple dimensions \n",
+    "such as miles per hour or meters per second."
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},