add notes about the source codes

Author: neverRare

README.md

@@ -25,3 +25,7 @@ deno task watch
 ```
 
 To stop this command, simply press Ctrl + C.
+
+## About the source codes
+
+With exception to `./src/main.ts`, every source codes in `./src/` are environment agnostic. Meaning it can be run on Deno as well. This makes it convenient to directly test codes by using `deno run`.