doc: update decisions template
markdown guidelines
-# Template
+# Template #
-## Issue
+## Issue ##
-## Constraints
+## Constraints ##
-## Assumptions
+## Assumptions ##
-## Considered Alternatives
+## Considered Alternatives ##
-## Decision
+## Decision ##
-## Argument
+## Argument ##
-## Implications
+## Implications ##
-## Related decisions
+## Related decisions ##
-## Notes
+## Notes ##
