📝 Update usage docs

Author: dwisiswant0

README.md

@@ -30,12 +30,13 @@ jobs:
         login: ${{ secrets.SONARQUBE_TOKEN }}
 ```
 
-You can change the analysis base directory by using the optional input `projectBaseDir` like this:
+You can change the analysis base directory and/ project key _(allowed characters: letters, numbers, -, _, . and :, with at least one non-digit.)_ by using the optional input like this:
 
 ```yaml
 uses: kitabisa/sonarqube-action@master
 with:
   projectBaseDir: my-custom-directory
+  projectKey: my-custom-project
 ```
 
 ## Secrets