reg-save: add page

pages/windows/reg-save.md

@@ -0,0 +1,11 @@
+# reg save
+
+> Save a registry key, its sub keys and values to a file.
+
+- Save a registry key, its sub keys and values to a specific file:
+
+`reg save {{key_name}} {{path/to/file}}`
+
+- Forcefully overwrite an existing file without a prompt:
+
+`reg save {{key_name}} {{path/to/file}} /y`