Update docker instructions in README and CONTRIBUTING

Author: eskombro

CONTRIBUTING.md

@@ -41,6 +41,7 @@ Each PR should pass the tests to be accepted.
 
 ```bash
 # Tests
+$ docker pull getmeili/meilisearch:latest # Fetch the latest version of MeiliSearch image from Docker Hub
 $ docker run -p 7700:7700 getmeili/meilisearch:latest ./meilisearch --master-key=masterKey --no-analytics
 $ bundle exec rspec
 ```

README.md

@@ -56,6 +56,7 @@ There are many easy ways to [download and run a MeiliSearch instance](https://do
 
 For example, if you use Docker:
 ```bash
+$ docker pull getmeili/meilisearch:latest # Fetch the latest version of MeiliSearch image from Docker Hub
 $ docker run -it --rm -p 7700:7700 getmeili/meilisearch:latest ./meilisearch --master-key=masterKey
 ```