Update README for generating app with template

Related: #938

Author: picandocodigo

README.md

@@ -86,7 +86,20 @@ Article.import
 ```
 
 You can generate a simple Ruby on Rails application with a single command
-(see the [other available templates](https://github.com/elastic/elasticsearch-rails/tree/master/elasticsearch-rails#rails-application-templates)):
+(see the [other available templates](https://github.com/elastic/elasticsearch-rails/tree/master/elasticsearch-rails#rails-application-templates)). You'll need to have an Elasticsearch cluster running on your system before generating the app. The easiest way of getting this set up is by running it with Docker with this command:
+
+```bash
+  docker run \
+    --name elasticsearch-rails-searchapp \
+    --publish 9200:9200 \
+    --env "discovery.type=single-node" \
+    --env "cluster.name=elasticsearch-rails" \
+    --env "cluster.routing.allocation.disk.threshold_enabled=false" \
+    --rm \
+    docker.elastic.co/elasticsearch/elasticsearch-oss:7.6.0
+```
+
+Once Elasticsearch is running, you can generate the simple app with this command:
 
 ```bash
 rails new searchapp --skip --skip-bundle --template https://raw.github.com/elasticsearch/elasticsearch-rails/master/elasticsearch-rails/lib/rails/templates/01-basic.rb

elasticsearch-rails/README.md

@@ -17,6 +17,7 @@ is compatible with the Elasticsearch `master` branch, therefore, with the next m
 | 2.x           | → | 2.x           |
 | 5.x           | → | 5.x           |
 | 6.x           | → | 6.x           |
+| 7.x           | → | 7.x           |
 | master        | → | master        |
 
 ## Installation
@@ -98,8 +99,8 @@ You should see the duration of the request to Elasticsearch as part of each log
 ### Rails Application Templates
 
 You can generate a fully working example Ruby on Rails application, with an `Article` model and a search form,
-to play with (it even downloads _Elasticsearch_ itself, generates the application skeleton and leaves you with
-a _Git_ repository to explore the steps and the code) with the
+to play with (it generates the application skeleton and leaves you with a _Git_ repository to explore the
+steps and the code) with the
 [`01-basic.rb`](https://github.com/elastic/elasticsearch-rails/blob/master/elasticsearch-rails/lib/rails/templates/01-basic.rb) template:
 
 ```bash

elasticsearch-rails/lib/rails/templates/01-basic.rb

@@ -44,7 +44,7 @@
 
 # ----- Check for Elasticsearch -------------------------------------------------------------------
 
-required_elasticsearch_version = '6'
+required_elasticsearch_version = '7'
 
 docker_command =<<-CMD.gsub(/\s{1,}/, ' ').strip
   docker run \
@@ -54,7 +54,7 @@
     --env "cluster.name=elasticsearch-rails" \
     --env "cluster.routing.allocation.disk.threshold_enabled=false" \
     --rm \
-    docker.elastic.co/elasticsearch/elasticsearch-oss:6.4.0
+    docker.elastic.co/elasticsearch/elasticsearch-oss:7.6.0
 CMD
 
 begin