Add Pyenv Python installation to the pipenv documentation

doc/install_pipenv.md

@@ -20,3 +20,40 @@ pipenv install
 pipenv shell
 ./silkaj
 ```
+
+## Manage Python versions with Pyenv
+
+If you have trouble with the pipenv install, may be the Python version installed on your system is not up to date.
+To install and manage easily multiple Python version, use Pyenv:
+
+### Install pyenv on your home
+```bash
+curl -L https://raw.githubusercontent.com/pyenv/pyenv-installer/master/bin/pyenv-installer | bash
+```
+
+Add in `~/.bash_profile`, in `~/.bashrc` on Fedora or Ubuntu:
+
+```bash
+export PATH="$HOME/.pyenv/bin:$PATH"
+eval "$(pyenv virtualenv-init -)"
+eval "$(pyenv init -)"
+export PYENV_ROOT="$HOME/.pyenv"
+```
+
+Reload your bash config:
+
+    source ~/.bashrc
+
+or
+
+    source ~/.bash_profile
+
+### Install Python version required
+
+    pyenv install 3.6.0
+
+### Select Python version for the current shell
+
+    pyenv shell 3.6.0
+
+Pipenv will search the `Pyenv` Python version chosen before the system version.