Fixup README and add .gitignore rules.

.gitignore

@@ -37,3 +37,9 @@ npm-debug.log
 
 # The default location of the generated database cluster.
 /data/
+
+# Directory used by `direnv` to hold `use flake`-generated profiles.
+/.direnv/
+
+# A symlink produced by default when running `nix build`.
+/result

README.md

@@ -13,7 +13,7 @@ $> nix develop
 An empty Postgres cluster is initialized at `/data`. To start the database, run
 the following:
 ```bash
-$> pg_ctl start -o --unix_socket_directories="$PGDATA"
+$> pg_ctl start -o --unix_socket_directories="$PWD/data"
 ```
 To shut the database down, run:
 ```bash
@@ -21,7 +21,7 @@ $> pg_ctl stop
 ```
 You can connect to this database from the project root directory by running:
 ```bash
-$> psql -h "$PWD"/data -d postgres
+$> psql -h "$PWD/data" -d postgres
 ```
 
 Afterward, you can run the Phoenix setup commands: