How to keep github fork repo in sync with main repo

This is how I keep my forked repo in sync with their main repos:

Create fork of the main repo.

Clone forked repo to your local machine:

git clone https://github.com/<username>/somerepo.git

Add main repo as another remote:

git remote add mainrepo https://github.com/<someurl>/somerepo.git

Fetch all the branches from mainrepo :

 git fetch mainrepo

Make sure that you're on your master (origin/master) :

git checkout master

Rebase your copy of master with main repo's master like this:

git rebase mainrepo/master