Small fixes on githubrepo

- Document how to install rugged --with-ssh in bundler
- Produce an error when using githubrepo without git as an output
- When no repository is defined, this is an error, not a debug message

CONTRIBUTING.md

@@ -119,6 +119,8 @@ bundle config set --local path 'vendor/bundle'
 bundle install
 ```
 
+Note: if you need to install rugged with ssh support, you can tell bundler so with `bundle config build.rugged --with-ssh`. Reinstall rugged with `bundle pristine rugged`
+
 ### Run your code
 ```bash
 bundle exec bin/oxidized

lib/oxidized/hook/githubrepo.rb

@@ -1,15 +1,21 @@
+require 'rugged'
+
 class GithubRepo < Oxidized::Hook
   def validate_cfg!
     raise KeyError, 'hook.remote_repo is required' unless cfg.has_key?('remote_repo')
   end
 
   def run_hook(ctx)
+    unless ctx.node.repo
+      log "Oxidized output is not git, can't push to remote", :error
+      return
+    end
     repo  = Rugged::Repository.new(ctx.node.repo)
     creds = credentials(ctx.node)
     url   = remote_repo(ctx.node)
 
     if url.nil? || url.empty?
-      log "No repository defined for #{ctx.node.group}/#{ctx.node.name}", :debug
+      log "No repository defined for #{ctx.node.group}/#{ctx.node.name}", :error
       return
     end