set DATABASE_URL for sqlx in development

Author: syphar

Diff for: .env.sample

@@ -1,5 +1,9 @@
 export DOCSRS_PREFIX=ignored/cratesfyi-prefix
 export DOCSRS_DATABASE_URL=postgresql://cratesfyi:password@localhost:15432
+
+# for local development with sqlx
+export DATABASE_URL="$DOCSRS_DATABASE_URL"
+
 export DOCSRS_LOG=docs_rs=debug,rustwide=info
 # To build with a PR that hasn't landed in a rust dist toolchain yet,
 # you can set this to the git sha of a try build: