update README

README.md

-# snakemake
+# Snakemake rules
 
-Repository for snakemake rules
\ No newline at end of file
+Repository for snakemake rules concerning tools and workflows

tools/README.md

+# Tools
+
+This directory contains all tool description that can be imported and used within Snakemake workflows
+
+Every rules for a tool should come with an example of use in a workflow as well as a `config.yaml`
+example file (usually containing default parameters that are set up on the `.rules` file itself).