Include openSUSE installation instructions for glow

[pizofreude]

Add installation instructions for openSUSE using Zypper.

• I have read CONTRIBUTING.md.
• I have created a discussion that was approved by a maintainer (for new features).
• Resolves issue Add glow installation for openSUSE #978

Installation Success

$ sudo zypper install glow
[sudo] password for root:
Looking for gpg keys in repository Brave Browser.
  gpgkey=https://brave-browser-rpm-release.s3.brave.com/brave-core.asc
Retrieving repository 'Brave Browser' metadata ..........................................................................................................................................[done]
Building repository 'Brave Browser' cache ...............................................................................................................................................[done]
Looking for gpg keys in repository network.
  gpgkey=https://download.opensuse.org/repositories/network/openSUSE_Tumbleweed/repodata/repomd.xml.key
Retrieving repository 'network' metadata ................................................................................................................................................[done]
Building repository 'network' cache .....................................................................................................................................................[done]
Retrieving repository 'packman-essentials' metadata .....................................................................................................................................[done]
Building repository 'packman-essentials' cache ..........................................................................................................................................[done]
Looking for gpg keys in repository openSUSE-Tumbleweed-Non-Oss.
  gpgkey=http://download.opensuse.org/tumbleweed/repo/non-oss/repodata/repomd.xml.key
Retrieving repository 'openSUSE-Tumbleweed-Non-Oss' metadata ............................................................................................................................[done]
Building repository 'openSUSE-Tumbleweed-Non-Oss' cache .................................................................................................................................[done]
Looking for gpg keys in repository openSUSE-Tumbleweed-Oss.
  gpgkey=http://download.opensuse.org/tumbleweed/repo/oss/repodata/repomd.xml.key
Retrieving repository 'openSUSE-Tumbleweed-Oss' metadata ................................................................................................................................[done]
Building repository 'openSUSE-Tumbleweed-Oss' cache .....................................................................................................................................[done]
Loading repository data...
Reading installed packages...
Resolving package dependencies...

The following NEW package is going to be installed:
  glow

1 new package to install.

Package download size:     5.4 MiB

Package install size change:
              |      18.8 MiB  required by packages that will be installed
    18.8 MiB  |  -      0 B    released by packages that will be removed

Backend:  classic_rpmtrans
Continue? [y/n/v/...? shows all options] (y): y
Preloading: glow-2.1.2-1.2.x86_64.rpm [done]
Preload finished. [success (4.4 KiB/s) ] ................................................................................................................................................[done]
Retrieving: glow-2.1.2-1.2.x86_64 (openSUSE-Tumbleweed-Oss)                                                                                                                (1/1),   5.4 MiB

Checking for file conflicts: ............................................................................................................................................................[done]
(1/1) Installing: glow-2.1.2-1.2.x86_64 .................................................................................................................................................[done]
Running post-transaction scripts ........................................................................................................................................................[done]

Installation Verification

 $ glow --version
glow version 2.1.2