reg-export: add page (#1927)

pages/windows/reg-export.md

@@ -0,0 +1,11 @@
+# reg export
+
+> Export the specified sub keys and values into a file.
+
+- Export all sub keys and values of a specific key:
+
+`reg export {{key_name}} {{path/to/file.reg}}`
+
+- Force overwriting of an existing file without prompt:
+
+`reg export {{key_name}} {{path/to/file.reg}} /y`