[BUG] Add foreman to docker config described in the README

**IMPORTANT: please make sure you ask yourself all intro questions and fill all sections of the template.**

**Before we start...:**

- [x] I checked the documentation and found no answer
- [x] I checked to make sure that this issue has not already been filed
- [x] I'm reporting the issue to the correct repository (for multi-repository projects)

**Expected behavior:**

Information about how to run dotenv_validator when you use foreman.

**Actual behavior:**

No informatino about how use dotenv_validator when you use foreman.

**Context and environment:**

We can update this part of the README: https://github.com/fastruby/dotenv_validator#if-you-use-docker-compose-read-this
to explain that it applies to foreman too.

For more context refer to this issue: https://github.com/fastruby/rails-template/issues/23

**I will abide by the [code of conduct](https://github.com/fastruby/dotenv_validator/blob/main/CODE_OF_CONDUCT.md)**