Refs: #179; Adding Contributing guidelines to README.md

README.md

@@ -422,6 +422,25 @@ but just to demonstrate the possibilities):
       {:ok, "<ul>\n<li>one\n</li>\n<li>two\n</li>\n</ul>\n* one* two", []}
 <!-- endmoduledoc: Earmark.Plugin -->
 
+## Contributing
+
+Pull Requests are happily accepted.
+
+Please be aware of one _caveat_ when correcting/improving README.md.
+
+Parts of the README.md are automatically generated by the mix task `readme`.
+
+The generated parts are delimited by comment pairs like
+
+    <!-- moduledoc: Earmark -->
+    <!-- endmoduledoc: Earmark -->
+
+or
+
+    <!-- doc: Earmark.as_html -->
+    <!-- enddoc: Earmark.as_html -->
+
+Please modify the associated docstrings instead.
 
 ## Author