docs: use .tab_stub() in examples, mention GT() args in guide

docs/examples/index.qmd

@@ -25,11 +25,12 @@ islands_mini = (
 )
 
 (
-    GT(islands_mini, rowname_col="name")
+    GT(islands_mini)
     .tab_header(
         title="Large Landmasses of the World",
         subtitle="The top ten largest are presented"
     )
+    .tab_stub(rowname_col="name")
     .tab_source_note(source_note="Source: The World Almanac and Book of Facts, 1975, page 406.")
     .tab_source_note(
         source_note=md("Reference: McNeil, D. R. (1977) *Interactive Data Analysis*. Wiley.")
@@ -108,9 +109,10 @@ wide_pops = (
 )
 
 (
-    GT(wide_pops, rowname_col="country_name", groupname_col="region")
+    GT(wide_pops)
     .tab_header(title="Populations of Oceania's Countries in 2000, 2010, and 2020")
     .tab_spanner(label="Total Population", columns=cs.all())
+    .tab_stub(rowname_col="country_name", groupname_col="region")
     .fmt_integer()
 )
 ```

docs/get-started/basic-stub.qmd

@@ -44,3 +44,13 @@ island_groups = islands.head(10).assign(group = ["subregion"] * 2 + ["country"]
     .tab_stubhead(label="landmass")
 )
 ```
+
+## GT convenience arguments
+
+Rather than using the `GT.tab_stub()` method, the `GT(rowname_col=..., groupname_col=...)` arguments
+provide a quick way to specify row names and groups.
+
+
+```{python}
+GT(island_groups, rowname_col="name", groupname_col="group")
+```