Help: Added a section about Misfin

res/about/help.gmi

@@ -1002,6 +1002,28 @@ timestamp = 1648809264
 * `version` (string): Version of the app that generated the archive.
 * `timestamp` (integer): Time of generation as a UNIX timestamp.
 
+# 7 Misfin
+
+Misfin is a messaging protocol that has been in the works since May 2023. Like Gemini, it relies on TLS and simple text-based requests, with 'text/gemini' as the content format.
+
+Lagrange has supported Misfin since version 1.18. You can import Misfin identity certificates and send messages using them. You will still need a Misfin mailbox where you can receive messages — servers are expected to verify the identity of unknown senders by checking if the sender's certificate matches the one provided by their server. 
+
+A Misfin identity certificate is a TLS client certificate where:
+
+* UID field specifies the mailbox name
+* subject alternative name(s) specify the domain name(s)
+* Common Name is the human-readable name
+
+You will need to import one or more of these before sending any messages.
+
+When sending a message, the Upload dialog opens in Misfin mode with "To" and "From" fields. As usual, the text editor in the dialog has basic Gemtext syntax highlighting, but otherwise the editor has nothing Misfin-specific. A toggle is provided if you want to send a copy of the message to yourself. Lagrange does not keep copies of sent messages because it does not maintain a local Misfin mailbox.
+
+When you click on a link with a "misfin://" URI, the dialog opens automatically with the recipient address prefilled.
+
+=> gemini://satch.xyz/misfin/  Misfin specification(s) and resources
+=> gemini://misfin.org/  Original Misfin specification
+=> gemini://bbs.geminispace.org/s/misfin  s/Misfin on BBS
+
 # Open source licenses
 
 => about:license