Use bundler and document it

.gitignore

@@ -3,3 +3,4 @@
 *~
 dev/run-g5kchecks/output/
 generators/run-g5kchecks/output/
+bundle

Gemfile.lock

@@ -95,4 +95,4 @@ DEPENDENCIES
   ruby-cute
 
 BUNDLED WITH
-   2.0.2
+   1.17.3

README.md

@@ -21,6 +21,17 @@ See also:
 * .gitlab-ci.yml, that automates various checks and the deployment of data files after each commit
 * doc/README.generators.md
 
+# Setup
+
+We use bundler to manage dependencies.
+
+```
+apt install bundler
+bundler install --standalone # this installs dependencies in the 'bundle' directory
+rake reference-api # or other commands
+```
+
+
 # Credentials
 
 all tools that require to authenticate against Grid'5000 use credentials from ~/.grid5000_api.yml. Example:

Rakefile

+require 'bundler/setup'
+
 if ENV['COV']
   require 'simplecov'
   SimpleCov.start