You have downloaded a compiled version of RoboMongo. Ordinarily such packages can be placed in either of 2 locations:
$HOME/bin
/usr/local/bin
I show the second option in this answer:
tar xvf robomongo-0.9.0-rc7-linux-x86_64-2b7a8ca.tar.gz
cd robomongo-0.9.0-rc7-linux-x86_64-2b7a8ca
sudo mv -v bin/* /usr/local/bin && sudo mv -v lib/* /usr/local/lib
If you then open the application with the command robomongo
from the command line you will then have an option (for Xenial at least) on the sidebar to right click and 'Add to Dash' or 'Lock to Launcher':

It is not very tidy but this archive is not a fully developed package as such and lacks neat installation and removal options. However removal can be done manually with the following two commands:
sudo rm -v /usr/local/bin/{qt.conf,robomongo}
sudo rm -rfv /usr/local/lib/{imageformats,libQt5DBus.so,\
libQt5PrintSupport.so.5.5.1,\
libicudata.so.54,libQt5DBus.so.5,libQt5Widgets.la,\
libicudata.so.54.1,libQt5DBus.so.5.5,libQt5Widgets.prl,\
libicui18n.so.54,libQt5DBus.so.5.5.1,libQt5Widgets.so,\
libicui18n.so.54.1,libQt5Gui.la,libQt5Widgets.so.5,\
libicuuc.so.54,libQt5Gui.prl,libQt5Widgets.so.5.5,\
libicuuc.so.54.1,libQt5Gui.so,libQt5Widgets.so.5.5.1,\
libQt5Core.la,libQt5Gui.so.5,libQt5XcbQpa.la,\
libQt5Core.prl,libQt5Gui.so.5.5,libQt5XcbQpa.prl,\
libQt5Core.so,libQt5Gui.so.5.5.1,libQt5XcbQpa.so,\
libQt5Core.so.5,libQt5PrintSupport.la,libQt5XcbQpa.so.5,\
libQt5Core.so.5.5,libQt5PrintSupport.prl,libQt5XcbQpa.so.5.5,\
libQt5Core.so.5.5.1,libQt5PrintSupport.so,libQt5XcbQpa.so.5.5.1,\
libQt5DBus.la,libQt5PrintSupport.so.5,platforms,\
libQt5DBus.prl,libQt5PrintSupport.so.5.5,platformthemes}
It takes a little bit of manual fiddling but this works nicely on my system and should on yours as well...