Fix doc links in README file to work with new website layout

Per report from Colin 't Hart

README.git

@@ -4,9 +4,9 @@ In a release or snapshot tarball of PostgreSQL, documentation files named
 INSTALL and HISTORY will appear in this directory.  However, these files are
 not stored in git and so will not be present if you are using a git checkout.
 If you are using git, you can view the most recent install instructions at:
-	http://developer.postgresql.org/docs/postgres/installation.html
+	http://www.postgresql.org/docs/devel/static/installation.html
 and the current release notes at:
-	http://developer.postgresql.org/docs/postgres/release.html
+	http://www.postgresql.org/docs/devel/static/release.html
 
 Users compiling from git will also need compatible versions of Bison, Flex,
 and Perl, as discussed in the install documentation.  These programs are not