Update README.md

Author: thiagodnf

README.md

@@ -2,8 +2,18 @@
 
 A comprehensive collection of Gnuplot examples
 
+## Line Charts
+
+![basic-line](https://user-images.githubusercontent.com/114015/102024554-bd7a5d80-3d60-11eb-8959-c6bff721ef47.png)
+
 ## Column and Bar Charts
 
-## Line Charts
+![basic-bar](https://user-images.githubusercontent.com/114015/102024574-dc78ef80-3d60-11eb-96c7-d934d82595d2.png)
+![basic-column](https://user-images.githubusercontent.com/114015/102024553-bce1c700-3d60-11eb-81a3-4edb9b00bdcd.png)
+![column-with-negative-values](https://user-images.githubusercontent.com/114015/102024556-bd7a5d80-3d60-11eb-9722-6ea7e9500009.png)
+![stacked-column](https://user-images.githubusercontent.com/114015/102024562-c10de480-3d60-11eb-80af-a928a155a64b.png)
 
 ## More Chart Types
+
+![spiderweb](https://user-images.githubusercontent.com/114015/102024561-c0754e00-3d60-11eb-9059-239e0086b942.png)
+![box-plot](https://user-images.githubusercontent.com/114015/102024555-bd7a5d80-3d60-11eb-8f59-22a579b6301b.png)