improve website links to the source install guide

[qgib]

Author Name: Gavin Fleming (@gubuntu)
Original Redmine Issue: 15665
Affected QGIS version: 2.16.3
Redmine category:documentation_and_help

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The install guide link on http://qgis.org/en/site/forusers/download.html points to master, which has changed radically from the 2.x releases, so it could be made clearer on the download page by provided links to the install buides for the different releases.

http://htmlpreview.github.io/?https://raw.github.com/qgis/QGIS/master/doc/INSTALL.html

[qgib]

Author Name: Jürgen Fischer (@jef-n)

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Issues with the website are tracked "here":https://github.com/qgis/QGIS-Website/issues

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• resolution was changed from to wontfix
• status_id was changed from Open to Closed