Update README, team postgres version to 10.7

[lbeaufort]

What we're after:
When we moved to aurora our documentation became out of date. We should get the documentation and get updated versions for the team.

Related tickets:

• Upgrade local CMS DB to use Postgres 11 fec-cms#3757
• Upgrade local eRegs DB to use Postgres 11 fec-eregs#499

Completion criteria:

• Update README, team postgres version to 10.7
• Double check the drivers
• Remind the team to update their versions
• Open any followup tickets as necessary

[hcaofec]

1. The description in README has been updated
2. Current PG drivers works fine
3. PG 10.13 has been installed on local computer, and works fine. Recommend team to upgrade local PG to latest 10. Here are the steps:
   brew services stop postgresql@9.6
brew uninstall postgresql@9.6.
brew install postgresql@10
   ---(update PATH in .bash_profile)---
   brew services start postgresql@10
4. It is recommend to create a new virtual environment
5. To test new database
   re-create cfdm_test, and run invoke create_sample_db
   run pytest
   psql cfdm_test

To check PG version:
which postgres
psql --version (show: 10.13)

[hcaofec]

This /.circleci/config.yml still has old version of Python and PG.
Follow-up ticket is created for further action if necessary.
#4425

PR was merged, so closing