doc: addd pre-requisites to scripts documentation

scripts/README.md

@@ -1,5 +1,16 @@
 This folder contains scripts that can be used in combination with hyperfines `--export-json` option.
 
+### Pre-requisites
+
+To make theses scripts work, you will need matplotlib installed. Just execute the following commands:
+
+```bash
+pip install matplotlib
+
+# If you're using python 3
+pip3 install matplotlib
+```
+
 ### Example:
 
 ``` bash