feat: update renderer docs

Author: skokenes

src/documentation/visualizations/about_rendering.malloynb

@@ -0,0 +1,53 @@
+>>>markdown
+# Rendering Documentation
+The latest and most up to date documentation for the Malloy renderer are now found in GitHub:
+
+- [Renderer Tag Documentation](https://github.com/malloydata/malloy/blob/main/packages/malloy-render/docs/renderer_tags_overview.md)
+- [Renderer Tag Cheatsheet](https://github.com/malloydata/malloy/blob/main/packages/malloy-render/docs/renderer_tag_cheatsheet.md)
+
+For developers wishing to implement custom renderers, a plugin system is available:
+- [Plugin System Overview](https://github.com/malloydata/malloy/blob/main/packages/malloy-render/docs/plugin-system.md)
+- [Plugin Quick Start](https://github.com/malloydata/malloy/blob/main/packages/malloy-render/docs/plugin-quick-start.md)
+- [Plugin API Reference](https://github.com/malloydata/malloy/blob/main/packages/malloy-render/docs/plugin-api-reference.md)
+>>>markdown
+ # Using Render Tags
+
+When Malloy runs a query, it returns two things.  The *results* of the query and *metadata* about the results.  The metadata are the schema for the results, including type information.  Malloy also provides a mechanism to tag things in the source code and return tags with this meta data. 
+
+In Malloy, anything that can be named can be tagged. A tag starts with a `#`. Tags that start on a new line attach the tag the thing on the following line. For more details about how tagging works, see the [Tags](../language/tags.malloynb) section.
+
+Malloy's rendering library interprets these tags to change how results are rendered. 
+
+## Tagging individual elements
+In the query below, the measure `percent_of_total` is tagged as a percentage. Any time `percent_of_total` is used in a query, Malloy's rendering library will be displayed as a percentage.
+>>>malloy
+source: flights is duckdb.table('../data/flights.parquet') extend {
+  measure:
+    flight_count is count()
+    # percent
+    percent_of_flights is flight_count / all(flight_count)
+}
+>>>malloy
+#(docs) size=small limit=5000
+run: flights -> {
+  group_by: carrier
+  aggregate: 
+    flight_count 
+    percent_of_flights
+}
+>>>malloy
+#(docs) size=small limit=5000
+run: duckdb.table('../data/flights.parquet') ->  {
+  group_by: carrier
+  aggregate: flight_count is count()
+}
+>>>markdown
+
+Simply adding `# bar_chart` before the query tags it and tells the rendering library to show the result as a bar chart. See the docs on the [Bar Chart tag](./bar_charts.malloynb) for more information.
+>>>malloy
+#(docs) size=large limit=5000
+# bar_chart
+run: duckdb.table('../data/flights.parquet') ->  {
+  group_by: carrier
+  aggregate: flight_count is count()
+}

src/documentation/visualizations/pivots.malloynb

@@ -5,6 +5,8 @@ Malloy's rederer has flexible and powerful way of pivoting data.
 ## Nesting first
 Malloy's ability to nest queries allows you to compute two levels of queries simultaneously.  The query below first groups airports by `state` and then groups by the type of facility (`fac_type`).  For each state we see count of all the facilities.
 >>>malloy
+## renderer_legacy
+
 run: duckdb.table('../data/airports.parquet') -> {
   group_by: state
   aggregate: facility_count is count()
@@ -186,3 +188,4 @@ run: flights -> {
   }
 }
 >>>markdown
+

src/table_of_contents.json

@@ -214,6 +214,15 @@
     },
     {
       "title": "Rendering Results",
+      "items": [
+        {
+          "title": "Overview",
+          "link": "/visualizations/about_rendering.malloynb"
+        }
+      ]
+    },
+    {
+      "title": "Rendering Legacy Docs",
       "items": [
         {
           "title": "Overview",