add "certified" to tools list

README.md

@@ -165,6 +165,7 @@ Repo mirrors:
 
 ## Tools
 - [CAPCOM](https://tildegit.org/solderpunk/CAPCOM) (Python) - Atom feed aggregator for gemini.
+- [certified](https://code.lag.net/robey/certified) (Python) - Generate TOFU TLS certificates for gemini servers.
 - [cl-yag](git://bitreich.org/cl-yag) (Common-Lisp) - Static site generator producing gemini, gopher and html.
 - [comitium](https://git.nytpu.com/comitium) (C) - A feed aggregator for gemini supporting many formats and protocols.
 - [gemini-pandoc-lua-filter](https://github.com/kr1sp1n/gemini-pandoc-lua-filter) (Lua) - lua filter for pandoc to output Gemini text.