add existing repo to github.md

1. Create a git repo locally, default branch_name:main or master based on the convention you are following>

git init -b <branch_name>

2. add all files to local git repo

git add --all

3. commiting the files

git commit -m

4. your remote repo URL

git remote add origin <REMOTE_URL>

5. verify the added remote

git remote -v

6. Push your changes to the remote repo

git push origin main