Add generation description for Registries

The script generates Registries, and it does not add descriptions. In
spite it's not required, it's a good idea to have a description of what
the registry is. Generate the field from the registry name.

Testing:
Put the modified script in phosphor-dbus-interfaces, built the project
and then generated registries in bmcweb from generated Jsons. They got
description fields populated:
```
$ git diff
diff --git a/redfish-core/include/registries/openbmc_logging_message_registry.hpp b/redfish-core/include/registries/openbmc_logging_message_registry.hpp
index 0333b4fd..b8f6f772 100644

Change-Id: I81c919fe1947949cbf69c5cb4481131fc8e0ee6f

--- a/redfish-core/include/registries/openbmc_logging_message_registry.hpp
+++ b/redfish-core/include/registries/openbmc_logging_message_registry.hpp
@@ -27,7 +27,7 @@ const Header header = {
     1,
     "OpenBMC Message Registry for xyz.openbmc_project.Logging",
     "en",
-    "",
+    "OpenBMC Message Registry for xyz.openbmc_project.Logging",
     "OpenBMC_Logging",
     "OpenBMC",
 };
diff --git a/redfish-core/include/registries/openbmc_state_cable_message_registry.hpp b/redfish-core/include/registries/openbmc_state_cable_message_registry.hpp
index 30f96254..2dee3e63 100644
--- a/redfish-core/include/registries/openbmc_state_cable_message_registry.hpp
+++ b/redfish-core/include/registries/openbmc_state_cable_message_registry.hpp
@@ -27,7 +27,7 @@ const Header header = {
     0,
     "OpenBMC Message Registry for xyz.openbmc_project.State.Cable",
     "en",
-    "",
+    "OpenBMC Message Registry for xyz.openbmc_project.State.Cable",
     "OpenBMC_StateCable",
     "OpenBMC",
 };
diff --git a/redfish-core/include/registries/openbmc_state_leak_detector_group_message_registry.hpp b/redfish-core/include/registries/openbmc_state_leak_detector_group_message_registry.hpp
index 4bf1e251..32d3498b 100644
--- a/redfish-core/include/registries/openbmc_state_leak_detector_group_message_registry.hpp
+++ b/redfish-core/include/registries/openbmc_state_leak_detector_group_message_registry.hpp
@@ -27,7 +27,7 @@ const Header header = {
     0,
     "OpenBMC Message Registry for xyz.openbmc_project.State.Leak.DetectorGroup",
     "en",
-    "",
+    "OpenBMC Message Registry for xyz.openbmc_project.State.Leak.DetectorGroup",
     "OpenBMC_StateLeakDetectorGroup",
     "OpenBMC",
 };
```

Change-Id: I8ed7b1117ba32bc545758175ccababf55527d363
Signed-off-by: Igor Kanyuka <ifelmail@gmail.com>
diff --git a/tools/sdbusplus/event.py b/tools/sdbusplus/event.py
index e843d4c..f8f950f 100644
--- a/tools/sdbusplus/event.py
+++ b/tools/sdbusplus/event.py
@@ -228,6 +228,7 @@
             "Language": f"{language}",
             "Messages": messages,
             "Name": f"OpenBMC Message Registry for {self.name}",
+            "Description": f"OpenBMC Message Registry for {self.name}",
             "OwningEntity": "OpenBMC",
             "RegistryPrefix": f"{registryName}",
             "RegistryVersion": f"{self.version}",