feat(docs): update features.md for plantuml and vega-lite examples

Signed-off-by: Max Wu <jackymaxj@gmail.com>

Author: jackycute

public/docs/features.md

@@ -313,11 +313,45 @@ GABc dedB|dedB dedB|c2ec B2dB|A2F2 G4:|
 g2gf g2Bd|g2f2 e2d2|c2ec B2dB|A2F2 G4:|
 ```
 
+### PlantUML
+```plantuml
+start
+if (condition A) then (yes)
+  :Text 1;
+elseif (condition B) then (yes)
+  :Text 2;
+  stop
+elseif (condition C) then (yes)
+  :Text 3;
+elseif (condition D) then (yes)
+  :Text 4;
+else (nothing)
+  :Text else;
+endif
+stop
+```
+
+### Vega-Lite
+```vega
+{
+  "$schema": "https://vega.github.io/schema/vega-lite/v3.json",
+  "data": {"url": "https://vega.github.io/editor/data/barley.json"},
+  "mark": "bar",
+  "encoding": {
+    "x": {"aggregate": "sum", "field": "yield", "type": "quantitative"},
+    "y": {"field": "variety", "type": "nominal"},
+    "color": {"field": "site", "type": "nominal"}
+  }
+}
+```
+
 > More information about **sequence diagrams** syntax [here](http://bramp.github.io/js-sequence-diagrams/).
 > More information about **flow charts** syntax [here](http://adrai.github.io/flowchart.js/).
 > More information about **graphviz** syntax [here](http://www.tonyballantyne.com/graphs.html)
 > More information about **mermaid** syntax [here](http://knsv.github.io/mermaid)
 > More information about **abc** syntax [here](http://abcnotation.com/learn)
+> More information about **plantuml** syntax [here](http://plantuml.com/index)
+> More information about **vega** syntax [here](https://vega.github.io/vega-lite/docs)
 
 Alert Area
 ---