Create remote-config-example.md

Provide some basic examples of using remotes to manipulate GitHub pull requests without a web browser.

.github/remote-config-example.md

+Run `git config -e` and add the block below then run `git fetch --all` to update all the GitHub pull request branches.
+
+```
+[remote "github"]
+        url = https://github.com/alpinelinux/aports.git
+        fetch = +refs/heads/*:refs/remotes/github/*
+        fetch = +refs/pull/*:refs/remotes/github/pr/*
+```
+
+After you have done this you can merge / squash / rebase / cherry-pick from the command line.
+
+For example, `git rebase master github/pr/XXX/head; git checkout master` would migrate all the commits from PR #XXX.
+
+You can then push the results back to the "origin" remote which should be the official Alpine Linux aports repository.