Document new rss command

README.md

@@ -4,10 +4,12 @@ This project tries to gather information about
 [open source](https://opensource.org/osd) contributions for a given
 organization.
 
-## Producing an HTML file
+## Producing output files
 
 First, make sure you installed dependencies, e.g. `composer install`.
 
+### HTML
+
 There is some scripting in place to generate an `HTML` page based on the data.
 It also contains `JSON-LD` output that may be useful if the page is public at
 some point.
@@ -16,6 +18,14 @@ You may want to try the following command.
 
     ./contriblog html > contributions.html
 
+### RSS
+
+There is also a way to produce RSS output.
+
+You may want to try the following command.
+
+    ./contriblog rss > rss.xml
+
 ## Adding entries
 
 - Use the helper, e.g. `./contriblog add`, or