Fix docker-compose file and document (#4621)

## Problem

- Running the command according to docker.md gives warning and error.
- Warning `permissions should be u=rw (0600) or less` is output when
executing `psql -h localhost -p 55433 -U cloud_admin`.
- `FATAL: password authentication failed for user "root”` is output in
compute logs.

## Summary of changes

- Add `$ chmod 600 ~/.pgpass` in docker.md to avoid warning.
- Add username (cloud_admin) to pg_isready command in docker-compose.yml
to avoid error.

---------

Co-authored-by: Tomoka Hayashi <tomoka.hayashi@ntt.com>

docker-compose/docker-compose.yml

@@ -189,7 +189,7 @@ services:
       - "/bin/bash"
       - "-c"
     command:
-      - "until pg_isready -h compute -p 55433 ; do
+      - "until pg_isready -h compute -p 55433 -U cloud_admin ; do
             echo 'Waiting to start compute...' && sleep 1;
          done"
     depends_on:

docs/docker.md

@@ -48,6 +48,7 @@ Creating docker-compose_storage_broker_1       ... done
 2. connect compute node
 ```
 $ echo "localhost:55433:postgres:cloud_admin:cloud_admin" >> ~/.pgpass
+$ chmod 600 ~/.pgpass
 $ psql -h localhost -p 55433 -U cloud_admin
 postgres=# CREATE TABLE t(key int primary key, value text);
 CREATE TABLE