docs: added the opt type to the commit style definition

docs/contribution_guide.md

@@ -35,10 +35,11 @@ notes
 
 A commits type can be one of the following:
 
-- **feat**: feature
-- **fix**: bugfix
-- **refactor**: nothing new added but code restructured, etc
-- **docs**: documentation changes
+- **feat:** feature
+- **fix:** bugfix
+- **refactor:** nothing new added but code restructured, etc
+- **docs:** documentation changes
+- **opt:** optimization changes
 
 The commit scope is kinda free, but it's a good idea to use scopes, that have been used before.
 Scopes can be nested like this: `scope >> subscope >> subscope`.