added documentation on firewall structure

docs/firewall-exporters.md

@@ -0,0 +1,48 @@
+# Firewall exporters documentation
+
+Firewall export feature is implemented trough a strategy pattern with an abstract class and a series of subclasses that implement the specific export logic for each firewall specific system:
+
+```mermaid
+ classDiagram
+ class FWType{
+        +getBanlist()
+}
+FWType <|-- Raw
+class Raw{ }
+FWType <|-- Iptables
+class Iptables{ }
+note for Iptables "implements the getBanlist method for iptables rules"
+```
+
+## Adding firewalls exporters
+
+To add a firewall exporter create a new python class in `src/firewall` that implements `FWType` class
+
+> example with `Yourfirewall` class in the `yourfirewall.py` file
+```python
+from typing_extensions import override
+from firewall.fwtype import FWType
+
+class Yourfirewall(FWType):
+
+    @override
+    def getBanlist(self, ips) -> str:
+        """
+        Generate raw list of bad IP addresses.
+
+        Args:
+            ips: List of IP addresses to ban
+
+        Returns:
+            String containing raw ips, one per line
+        """
+        if not ips:
+            return ""
+        # Add here code implementation
+```
+
+Then add the following to the `src/server.py` and `src/tasks/top_attacking_ips.py`
+
+```python
+from firewall.yourfirewall import Yourfirewall
+```