update styler user guide for text_gradient (pandas-dev#41661)

Author: attack68

doc/source/user_guide/style.ipynb

@@ -1012,7 +1012,8 @@
     " - [.highlight_min][minfunc] and [.highlight_max][maxfunc]: for use with identifying extremeties in data.\n",
     " - [.highlight_between][betweenfunc] and [.highlight_quantile][quantilefunc]: for use with identifying classes within data.\n",
     " - [.background_gradient][bgfunc]: a flexible method for highlighting cells based or their, or other, values on a numeric scale.\n",
-    " -  [.bar][barfunc]: to display mini-charts within cell backgrounds.\n",
+    " - [.text_gradient][textfunc]: similar method for highlighting text based on their, or other, values on a numeric scale.\n",
+    " - [.bar][barfunc]: to display mini-charts within cell backgrounds.\n",
     " \n",
     "The individual documentation on each function often gives more examples of their arguments.\n",
     "\n",
@@ -1022,6 +1023,7 @@
     "[betweenfunc]: ../reference/api/pandas.io.formats.style.Styler.highlight_between.rst\n",
     "[quantilefunc]: ../reference/api/pandas.io.formats.style.Styler.highlight_quantile.rst\n",
     "[bgfunc]: ../reference/api/pandas.io.formats.style.Styler.background_gradient.rst\n",
+    "[textfunc]: ../reference/api/pandas.io.formats.style.Styler.text_gradient.rst\n",
     "[barfunc]: ../reference/api/pandas.io.formats.style.Styler.bar.rst"
    ]
   },
@@ -1098,14 +1100,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Background Gradient"
+    "### Background Gradient and Text Gradient"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "You can create \"heatmaps\" with the `background_gradient` method. These require matplotlib, and we'll use [Seaborn](https://stanford.edu/~mwaskom/software/seaborn/) to get a nice colormap."
+    "You can create \"heatmaps\" with the `background_gradient` and `text_gradient` methods. These require matplotlib, and we'll use [Seaborn](https://stanford.edu/~mwaskom/software/seaborn/) to get a nice colormap."
    ]
   },
   {
@@ -1120,19 +1122,31 @@
     "df2.style.background_gradient(cmap=cm)"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "df2.style.text_gradient(cmap=cm)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "[.background_gradient][bgfunc] has a number of keyword arguments to customise the gradients and colors. See its documentation.\n",
+    "[.background_gradient][bgfunc] and [.text_gradient][textfunc] have a number of keyword arguments to customise the gradients and colors. See the documentation.\n",
     "\n",
-    "[bgfunc]: ../reference/api/pandas.io.formats.style.Styler.background_gradient.rst"
+    "[bgfunc]: ../reference/api/pandas.io.formats.style.Styler.background_gradient.rst\n",
+    "[textfunc]: ../reference/api/pandas.io.formats.style.Styler.text_gradient.rst"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
+    "### Set properties\n",
+    "\n",
     "Use `Styler.set_properties` when the style doesn't actually depend on the values. This is just a simple wrapper for `.applymap` where the function returns the same properties for all cells."
    ]
   },