Update Clearnet on appendix A

src/appendix_a.md

@@ -1,3 +1,3 @@
 ## Clearnet
 
-WIP
+Clearnet is the publicly available portion of the internet. It is the part of the web that is easily accessible using standard web browsers and does not require any special configurations or tools to access. Unlike the deep web or dark web, the clearnet is open and not hidden behind special configurations.