"Actually Using Git": can't branch on an empty repo

[jadrian]

On tutorials/actually-using-git/lessons/conflicting-branches.md , there are three reasonable ways to initialize a repo:

1. Reuse an existing repo
2. Create a new repo on Github and then clone it
3. Use git init

If a participant uses the third option (git init) and then, following the directions, immediately tries to create a new branch, they'll get an error:

fatal: Not a valid object name: 'master'.

Instead, they should create a dummy readme.md, add and commit it, and then proceed.

The instructions should be clarified for folks who choose the third option.