Add rules for individual localized sources

Makefile

@@ -4,9 +4,17 @@
 
 SWG=swg
 
-all: output/
+all: output/en/ output/pt/
+
+en: output/en/
+
+pt: output/pt/
+
+output/en/: src/en/
 	$(SWG) src/en/
 	mv src/en/output output/en
+
+output/pt/: src/pt/
 	$(SWG) src/pt/
 	mv src/pt/output output/pt
 

README.md

@@ -27,3 +27,8 @@ To delete previously built pages, run the following command:
 ```sh
 $ make clean
 ```
+
+You can also build the English version only with:
+```sh
+$ make en       # or use `pt' to build Portuguese sources
+```