update linux install instructions

Author: trevor-polidore

gitkraken-client/how-to-install.md

@@ -62,7 +62,7 @@ GitKraken Client data is stored in `/Users/{user}/.gitkraken` == `~/.gitkraken`.
 GitKraken Client has a simple package available for Debian based distributions.
 ```
 wget https://release.gitkraken.com/linux/gitkraken-amd64.deb
-sudo dpkg -i gitkraken-amd64.deb
+sudo apt install gitkraken-amd64.deb
 ```
 Or [download the file](https://gitkraken.com/download/linux-deb).
 
@@ -76,10 +76,12 @@ Or [download the file](https://gitkraken.com/download/linux-gzip).
 ### .rpm
 ```
 wget https://release.gitkraken.com/linux/gitkraken-amd64.rpm
-sudo yum install ./gitkraken-amd64.rpm
+sudo dnf install ./gitkraken-amd64.rpm
 ```
 Or [download the file](https://gitkraken.com/download/linux-rpm).
 
+Note: for older distros that do not have ```dnf```, you should use ```yum``` instead.
+
 ### Snap
 
 Snap is an easy-to-install package for Linux distributions (supported versions above). Get it from the snap store or [Snapcraft.io](https://snapcraft.io/gitkraken).