docs: add caddy docs (#423)

Signed-off-by: Xe Iaso <me@xeiaso.net>

test/caddy/start.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+# If the transient local TLS certificate doesn't exist, mint a new one
+if [ ! -f ../pki/caddy.local.cetacean.club/cert.pem ]; then
+  # Subshell to contain the directory change
+  (
+    cd ../pki \
+    && mkdir -p caddy.local.cetacean.club \
+    && \
+    # Try using https://github.com/FiloSottile/mkcert for better DevEx,
+    # but fall back to using https://github.com/jsha/minica in case
+    # you don't have that installed.
+    (
+      mkcert \
+        --cert-file ./caddy.local.cetacean.club/cert.pem \
+        --key-file ./caddy.local.cetacean.club/key.pem caddy.local.cetacean.club \
+      || go tool minica -domains caddy.local.cetacean.club
+    )
+  )
+fi
+
+docker compose up --build