Update INSTALL.md

* First note that there is easier installation guide available
* Mention Fedora packages
* Update Debian package links
* Use curl instead of wget as it seems to be more often installed by
default
* Tell to upgrade pip if it fails without doing anything
* Remove duplication of Debian/Fedora package upgrading
* Remove space from pip
Merge pull request #830 from Mkaysi/install

Update INSTALL.md