Adds content for ci and badge

Adds about GitLab CI Adds Registry Adds diagram Adds CI badge

Closes #1 (closed)

content/concepts.md

 ## Concepts
-- *Continouos Integration*: software development practice where code is integrated regularly. 
+- *Continouos Integration*: software development practice where code is
+integrated regularly.
+
 - Integration usually includes building and testing  
-- *Continouos Deployment*: closely related to CI but also implies releasing integrated code into production
-- References: 
+
+- *Continouos Deployment*: closely related to CI but also implies releasing
+integrated code into production
+
+- References:
   - [Martin Fowler](http://www.martinfowler.com/articles/continuousIntegration.html)
   - [ThoughtWorks](https://www.thoughtworks.com/continuous-integration)
-  - [Agile Alliance](https://www.agilealliance.org/glossary/continuous-integration/) 
+  - [Agile Alliance](https://www.agilealliance.org/glossary/continuous-integration/)