Update README.md to include working install instructions

I updated the "Creating Your Own Aphostrophe Project: The Easy Way" paragraph to be more clear and mainly to update the `git clone` url (using the ssh endpoint results in a `Permission denied (publickey)` error, the `https` version should be used instead).

I've also updated the suggested way to update the remote `origin` as it should be done with git tools (that is `git remote set-url`) instead of editing the `.git/config` file by hand (as any mistake could break the repo itself).

Let me know if I missed something, thanks.
-- Lex