dir didn't match the command

directory name is `postgresql` and command says `cd postgres`.
Copy paste doesn't work :)
diff --git a/containers/README.md b/containers/README.md
index 0bdc74b..ec141d9 100644
--- a/containers/README.md
+++ b/containers/README.md
@@ -17,7 +17,7 @@
 To build and run the database container:
 
 ```
-$ cd postgres; make build && make run
+$ cd postgresql; make build && make run
 ```
 
 #### XOS Container