add example how to write own rules

README.md

@@ -55,3 +55,21 @@ rspamd can sign outgoing mails with dkim. the following steps are necessary:
 
 ## spam learning
 To train ham/spam from move actions from/to junk folder, `imap_sieve` needs to be enabled in dovecot.
+
+## writing manual rules
+example:
+```
+files:
+  "/etc/rspamd/local.d/rspamd.lua":
+    owner: _rspamd
+    group: root
+    mode: "0640"
+    content: |
+      -- Generica
+      config['regexp']['SUBJECT_GENERICA'] = {
+        re = 'Subject=/Die besten Generica/Hu',
+        description = 'Subject contains "Die besten Generica"',
+        score = 13.37,
+        group = 'headers'
+      }
+```