Added documentation for snippet arguments

Added documentation, the only resource available for this feature, a post on the forum and the PR : https://github.com/caddyserver/caddy/pull/3423

src/docs/markdown/caddyfile/concepts.md

@@ -276,6 +276,27 @@ import redirect
 
 The [`import`](/docs/caddyfile/directives/import) directive can also be used to include other files in its place. As a special case, it can appear almost anywhere within the Caddyfile.
 
+The [`import`](/docs/caddyfile/directives/import) directive supports the arguments :
+
+```caddy
+(log_common) {
+  log {
+    output file /var/log/caddy/{args.0}.access.log
+  }
+}
+```
+
+And then you can reuse it anywhere with parameters: 
+
+```caddy-d
+a.example.com {
+  import log_common a.example.com
+}
+
+b.example.com {
+  import log_common b.example.com
+}
+```
 
 
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