Add documentation for default plugins installed

[ketozhang]

A few plugins are installed by default:

pyenv-installer/bin/pyenv-installer

Lines 46 to 51 in 49fba59

	checkout "${GITHUB}/pyenv/pyenv.git" "${PYENV_ROOT}" "${PYENV_GIT_TAG:-master}"
	checkout "${GITHUB}/pyenv/pyenv-doctor.git" "${PYENV_ROOT}/plugins/pyenv-doctor" "master"
	checkout "${GITHUB}/pyenv/pyenv-installer.git" "${PYENV_ROOT}/plugins/pyenv-installer" "master"
	checkout "${GITHUB}/pyenv/pyenv-update.git" "${PYENV_ROOT}/plugins/pyenv-update" "master"
	checkout "${GITHUB}/pyenv/pyenv-virtualenv.git" "${PYENV_ROOT}/plugins/pyenv-virtualenv" "master"
	checkout "${GITHUB}/pyenv/pyenv-which-ext.git" "${PYENV_ROOT}/plugins/pyenv-which-ext" "master"

Please,

• Add to README, a list of the default plugin installed by the installer
• Add an option to disable installing these plugin, or don't install any plugins by default.

[izzatkarimov]

Hello, is the issue solved?
Or can I go ahead and solve it?

[ketozhang]

No, go ahead.