Git: How to delete a branch

How do you create a temporary branch to do some work in (e.g, a feature branch), and then when you have merged it to master and are done with it, how do you delete it, both locally and remotely?

Let's create a simple repo to experiment with. We'll add just one file to it.

mkdir myprj
cd myprj
git init
vim README.md
git add README.md
git commit -m "adding a README"

Okay, this will be our "central repo". Let's clone it, create a branch and do some work on it.

git clone myprj myprj2
cd myprj2
git branch install_notes
git checkout install_notes
vim README.md
git commit -a -m "Adding some installation notes"
git push origin install_notes
# Oops, forgot to set upstream
git push --set-upstream origin install_notes

The branch install_notes now exists locally and in the "central repo". Let's merge it and then delete it locally and also remotely. Before we get started though, here are all of our local and remote branches:

marcus$ git branch -avv
    * install_notes                6a5ed4c [origin/install_notes] Adding some installation notes
    master                       27c8a05 [origin/master] adding a README
    remotes/origin/HEAD          -> origin/master
    remotes/origin/install_notes 6a5ed4c Adding some installation notes
    remotes/origin/master        27c8a05 adding a README

First, let's switch back to master and try to delete install_notes:

marcus$ git checkout master
    Switched to branch 'master'
    Your branch is up-to-date with 'origin/master'.
marcus$ git branch -d install_notes
    warning: deleting branch 'install_notes' that has been merged to
            'refs/remotes/origin/install_notes', but not yet merged to HEAD.
    Deleted branch install_notes (was 6a5ed4c).

Hmm. It gave a warning, but proceeded to delete the branch anyways. Well, let's try to check it back out.

marcus$ git checkout -b install_notes origin/install_notes
    Branch install_notes set up to track remote branch install_notes from origin.
    Switched to a new branch 'install_notes'
marcus$ git checkout master
    Switched to branch 'master'
    Your branch is up-to-date with 'origin/master'.
marcus$ git merge install_notes
    Updating 27c8a05..6a5ed4c
    Fast-forward
    README.md | 4 ++++
    1 file changed, 4 insertions(+)

Okay, now we can delete the branch.

marcus$ git branch -d -r origin/install_notes
Deleted remote branch origin/install_notes (was 6a5ed4c).
marcus$ git branch -d install_notes
Deleted branch install_notes (was 6a5ed4c).

And now my branches look like this

marcus$ git branch -avv
    * master                6a5ed4c [origin/master: ahead 1] Adding some installation notes
    remotes/origin/HEAD   -> origin/master
    remotes/origin/master 27c8a05 adding a README