add installation instructions for Gedit3 to README file

Author: oliver

README

@@ -3,4 +3,18 @@ File Search Plugin for Gedit
 This is a search plugin for Gedit to search for a text inside a directory.
 
 The plugin was tested with Gedit 3.4.1 under Ubuntu 12.04. It might also work under other versions of Gedit 3.
+
 Note that Gedit 2 and older are not supported by this plugin any more (there is an old version of this plugin available, though, which supports Gedit 2).
+
+
+Installation
+-------------
+* download the plugin [1]
+* unpack the tgz file
+* copy the contents of the gedit-file-search folder to ~/.local/share/gedit/plugins/ (create that folder if necessary)
+* start Gedit, go to Edit -> Preferences -> Plugins, and enable "File Search"
+
+  [1]: http://cloud.github.com/downloads/oliver/gedit-file-search/gedit-file-search-0.5.tgz
+
+
+Use Search -> Find in files, or right-click in a document and select Search files... to open the search dialog.