Update README.md

Author: thiagodnf

README.md

@@ -4,16 +4,28 @@ A comprehensive collection of Gnuplot examples
 
 ## Line Charts
 
+### Basic Line
+
 ![basic-line](https://user-images.githubusercontent.com/114015/102024554-bd7a5d80-3d60-11eb-8959-c6bff721ef47.png)
 
 ## Column and Bar Charts
 
+### Basic Bar
 ![basic-bar](https://user-images.githubusercontent.com/114015/102024574-dc78ef80-3d60-11eb-96c7-d934d82595d2.png)
+
+### Basic Column
 ![basic-column](https://user-images.githubusercontent.com/114015/102024553-bce1c700-3d60-11eb-81a3-4edb9b00bdcd.png)
+
+### Column with Negative Values
 ![column-with-negative-values](https://user-images.githubusercontent.com/114015/102024556-bd7a5d80-3d60-11eb-9722-6ea7e9500009.png)
+
+### Stacked Column
 ![stacked-column](https://user-images.githubusercontent.com/114015/102024562-c10de480-3d60-11eb-80af-a928a155a64b.png)
 
 ## More Chart Types
 
+### Spiderweb
 ![spiderweb](https://user-images.githubusercontent.com/114015/102024561-c0754e00-3d60-11eb-9059-239e0086b942.png)
+
+### Box Plot
 ![box-plot](https://user-images.githubusercontent.com/114015/102024555-bd7a5d80-3d60-11eb-8f59-22a579b6301b.png)