Doc: update pgindent/README.

I missed updating this when we pulled pg_bsd_indent into the tree.

Author: tglsfdc

src/tools/pgindent/README

@@ -10,9 +10,9 @@ http://adpgtech.blogspot.com/2015/05/running-pgindent-on-non-core-code-or.html
 
 PREREQUISITES:
 
-1) Install pg_bsd_indent in your PATH.  Fetch its source code with
-   git clone https://git.postgresql.org/git/pg_bsd_indent.git
-   then follow the directions in README.pg_bsd_indent therein.
+1) Install pg_bsd_indent in your PATH.  Its source code is in the
+   sibling directory src/tools/pg_bsd_indent; see the directions
+   in that directory's README file.
 
 2) Install perltidy.  Please be sure it is version 20170521 (older and newer
    versions make different formatting choices, and we want consistency).