Documented CSV columns in README

Resolves #1

Author: schmengler

README.md

@@ -22,6 +22,12 @@ END,release,1553682979.3,0.8
 END,deploy,1553682979.3,4.9
 ```
 
+The columns are:
+- `BEGIN` or `END`, marking time where a task started or finished
+- task name
+- Unix timestamp (as float)
+- Duration of task in seconds (only in `END` rows)
+
 ## Installation
 
 1. Require via composer
@@ -97,4 +103,4 @@ The MIT License (MIT). Please see [License File](LICENSE.txt) for more informati
 [link-code-quality]: https://scrutinizer-ci.com/g/integer-net/deployer-timer
 [link-downloads]: https://packagist.org/packages/integer-net/deployer-timer
 [link-author]: https://github.com/schmengler
-[link-contributors]: ../../contributors
+[link-contributors]: ../../contributors