Make instructions more clear. (#2)

Make docker build instructions more easier.

Author: hackintoshrao

README.md

@@ -18,7 +18,8 @@ Collection of tests to detect resource leaks, gauge performance problems and ove
 - Build and Run
 
   ```sh
-  $ docker build -t minio/mint:alpha
+  $ cd mint
+  $ docker build -t minio/mint:alpha .
   $ docker run -e ENDPOINT=play.minio.io:9000 -e ACCESS_KEY=Q3AM3UQ867SPQQA43P2F  -e SECRET_KEY=zuf+tfteSlswRu7BJ86wekitnifILbZam1KYY3TG -e ENABLE_HTTPS=1  mint:alpha
   ```