Add installation instructions to README

Add installation instructions to README.

[ci skip]

README.md

@@ -1,9 +1,68 @@
 # OpenProject XLS Export Plugin
 
-Export issue lists as Excel spreadsheets (.xls). This plugin adds a link below each issue list which allows downloading the list as Excel spreadsheet.
+Enables work package export as Excel spreadsheets (.xls). This plugin allows work package export as Excel document in the work package list.
 
-Support for exporting cost entries and cost reports is not yet migrated to Rails 3 and disabled.
+To export work packages in the work package list, select the `Settings` menu button (gear icon) and select `Export ...` from the dropdown menu.
+Choose either `XLS` or `XLS with descriptions` (to export the work package list with the work package descriptions) to export the work packages shown in the work package list.
 
-# Issue Tracker
 
-https://www.openproject.org/projects/export/issues
+Requirements
+------------
+
+The OpenProject XLS-Export plugin requires the [OpenProject Core](https://github.com/opf/openproject/) to be in the same version as the plugin.
+
+Installation
+------------
+
+To install the OpenProject XLS-Export plugin you need to add the following line to the `Gemfile.plugins` in your OpenProject folder (if you use a different OpenProject version than OpenProject 5, adapt `:branch => "stable/5"` to your OpenProject version):
+
+`gem "openproject-xls_export", git: "https://github.com/finnlabs/openproject-xls_export.git", :branch => "stable/5"`
+
+Afterwards, run:
+
+`bundle install`
+
+Deinstallation
+--------------
+
+Remove the line
+
+`gem "openproject-xls_export", git: "https://github.com/finnlabs/openproject-xls_export.git", :branch => "stable/5"`
+
+from the file `Gemfile.plugins` and run:
+
+`bundle install`
+
+Bug Reporting
+-------------
+
+If you find any bugs, you can create a bug ticket at
+https://community.openproject.org/projects/export
+
+Development
+-----------
+
+To contribute, you can create pull request on the official repository at
+`https://github.com/finnlabs/openproject-xls_export`
+
+Copyright
+-------
+
+* Copyright (C) 2010-2015 OpenProject GmbH
+
+Licence
+-------
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.