migrations: add readme_file_path to versions

The readme_file_path column is added to the versions table, which will be
used to determine the markup type that the readme is written in.

Change-Id: I2cfcd97a6e9e4bd102d1506916d5543e717e1927
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/451769
Reviewed-by: Robert Findley <rfindley@google.com>

migrations/000028_add_readme_filepath.down.sql

@@ -0,0 +1,9 @@
+-- Copyright 2019 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE versions DROP COLUMN readme_file_path;
+
+END;

migrations/000028_add_readme_filepath.up.sql

@@ -0,0 +1,9 @@
+-- Copyright 2019 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE versions ADD COLUMN readme_file_path TEXT;
+
+END;