update Makefile

Author: vinta

Diff for: Makefile

@@ -1,12 +1,14 @@
 site_install:
-	pip install mkdocs==0.16.3
-	pip install mkdocs-material==1.12.2
+	pip install -r requirements.txt
 
 site_link:
 	ln -sf $(CURDIR)/README.md $(CURDIR)/docs/index.md
 
 site_preview: site_link
 	mkdocs serve
 
+site_build: site_link
+	mkdocs build
+
 site_deploy: site_link
 	mkdocs gh-deploy --clean