public: Add documents

This adds the index.gmi and xmpp.gmi documents for the mint.lgbt Gemini
capsule

public/index.gmi

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+```The mint.lgbt leaf logo
+      .::.
+    .:=+=-..
+  ..=+**---:..
+  .=++++::....
+ .:===++.::::..
+..--====::::::..
+..-----=::::::..
+ ..::---::::-..
+  ..:::-:--:..
+     ......
+```
+
+# Welcome to mint.lgbt!
+
+mint.lgbt is a service provider built for and run by LGBTQIA+ people. Founded in 2020, we're a non-profit run by Lux and Luna focusing on providing privacy-respecting FOSS services.
+
+## Services
+
+=> xmpp.gmi XMPP
+
+## See also
+
+=> https://mint.lgbt/ mint.lgbt (HTTPS)
+=> gemini://nixgoat.me/ Lux's Gemini Capsule

public/xmpp.gmi

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+=> / ← Go back
+
+```The XMPP logo
+:*+-.            .-=*-
+ =*+=--        +****+
+  ==+--.      .***+=.
+   :-=--      +**=:
+     -=--    =**-.
+      .-=-.:+*=.
+        .==-=.
+      ...    ...
+```
+
+# The mint.lgbt XMPP server
+
+XMPP (originally named Jabber) is an open, federated messaging protocol. mint.lgbt offers a public server using the Prosody software. If you want to sign up, install a client and use in-band registration with the address "mint.lgbt".
+
+=> https://xmpp.org/software/ XMPP Software (HTTPS)
+=> https://compliance.conversations.im/server/mint.lgbt/ XMPP Specifications compliance (HTTPS)
+=> https://prosody.im/ Prosody Home Page (HTTPS)