CSE-1: link rules in main readme

Author: SeidChr

README.md

@@ -19,6 +19,8 @@ The severity of individual rules may be configured using [rule set files](https:
 in Visual Studio 2015 or newer. **Settings.StyleCop** is not supported, but a **stylecop.json** file may be used to
 customize the behavior of certain rules. See [Configuration.md](documentation/Configuration.md) for more information.
 
+For Documentation and reasoning on the rules themself, go to [Documentation.md](DOCUMENTATION.md).
+
 For users upgrading from StyleCop Classic, see [KnownChanges.md](https://github.com/DotNetAnalyzers/StyleCopAnalyzers/tree/master/documentation/KnownChanges.md)
 for information about known differences which you may notice when switching to StyleCop Analyzers.