fix the graph in the readme

README.md

@@ -151,6 +151,7 @@ are discarded. The number of discarded flows is written in the cli at the end of
 * timewindow numbers may be negative if a flow is found with a flow timestamp < timestamp of the first flow seen
 * if a slips alert exists in parts of 2 timewindows
 * what we're doing here is marking bith timewindows as malicious 
+```
 
                 1:30                   2:30
                  │      slips alert     │
@@ -159,6 +160,7 @@ are discarded. The number of discarded flows is written in the cli at the end of
  ├───────────────────────────┼────────────────────────────┤
  │             tw 1                 tw 2                  │
 
+```
 ---