Add intallation guide.

README.md

@@ -9,6 +9,20 @@ Limitations:
  It expects the classes of the hierarchy to have at least one slot named differently.  
  It does not fully follow the JSON specification.
 
+
+## Installing trivial-json-codec
+
+Since this project is not yet available in the latest [QuickLisp](https://www.quicklisp.org/beta/ "QuickLisp") distribution, it has to be copied to your local-projects folder:
+```bash
+cd $HOME/quicklisp/local-projects
+git clone https://gitlab.com/ediethelm/trivial-json-codec.git
+```
+
+After the files are copied, we can use [QuickLisp](https://www.quicklisp.org/beta/ "QuickLisp") to load trivial-json-codec:
+```lisp
+(ql:quickload :trivial-json-codec)
+```
+
 ## Working Example
 
 The following code demonstrates the use-case for this library.