explained what files in fs/ folder are for

fs/README.md

@@ -0,0 +1,29 @@
+
+In general, files in here ought to provide exactly tow functions:
+```
+    yl_speak_up.input_fs_<FILE_NAME> = function(player, formname, fields)
+        -- react to whatever input the player supplied;
+        -- usually show another formspec
+        return
+    end
+```
+and:
+```
+    yl_speak_up.get_fs_<FILE_NAME> = function(player, param)
+        -- return a formspec string
+        return formspec_string
+    end
+```
+
+Additional (local) helper functions may be included if they are only used
+by those two functions above and not used elsewhere in the mod.
+That is not a technical requirement but mostly for keeping things clean.
+These functions are usually *not* declared as local and may be overridden
+from outside if needed.
+
+There may be no function for handling input if the formspec only displays
+something and only offers a back button or buttons to other formspecs.
+
+The actual displaying of the formspecs and calling of these functions happens
+in `show_fs.lua`.
+