====edited===
Steve posted while I was writing, so apology for repeating, also
I have included some additional links to documentation, for anyone
willing to take the time to read it.
===end edit===
Based on this, it is not available for the current stable version
of Debian,...I looked at the link as well, and it says it is only
available for "Debian stretch" , testing and "SID".
Exact hits
Package neovim
stretch (testing) (editors): heavily refactored vim fork
0.1.7-3: amd64 arm64 armel armhf i386 mips mips64el mipsel ppc64el s390x
sid (unstable) (editors): heavily refactored vim fork
0.1.7-3: alpha amd64 arm64 armel armhf hppa i386 kfreebsd-amd64 kfreebsd-i386 mips mips64el mipsel powerpc ppc64 ppc64el s390x sparc64
0.1.5-8 [debports]: x32
Changing ones sources to different mirrors, will not change the fact
that it is not available for Debian Jessie (stable) .
If the OP wanted to upgrade their system to Debian Stretch (testing)
it would be available,
That is a decision for the OP , if it is that important to have the package.
Since :
by Tamim » I know little about GNU/Linux. Please help me install packages with 'apt-get'.
It also would be a good idea to maybe read:
https://wiki.debian.org/DontBreakDebian
and also read some of the documentation on what Debian testing is, and who should or shouldn't use it, before deciding to upgrade or not.
===
On "please help me install packages with 'apt-get'"
I would suggest reading these to anybody "new" to Debian.
https://wiki.debian.org/DebianPackageManagement
Is a good place to start, there are many details.
Also :
https://www.debian.org/doc/manuals/debi ... ls.en.html
There is more using this search string:
How to install packages using apt-get on Debian