readme: Add Link to Manual

Author: johannes-wolf

README.md

@@ -59,7 +59,7 @@ CeTZ-Plot requires CeTZ version ≥ 0.5.0!
 
 ## Usage
 
-For information, see the [manual (stable)](https://github.com/cetz-package/cetz-plot/blob/stable/manual.pdf?raw=true).
+For information, see the [manual ](./manual.pdf?raw=true).
 
 To use this package, simply add the following code to your document:
 ```