doc: expand information on venv usage

Resolves: #2333

docs/docs/basic-usage.md

@@ -64,6 +64,55 @@ $ poetry add pendulum
 It will automatically find a suitable version constraint **and install** the package and subdependencies.
 
 
+## Using your virtual environment
+
+By default, poetry creates a virtual environment in `{cache-dir}/virtualenvs` (`{cache-dir}\virtualenvs` on Windows).
+You can change the [`cache-dir`](/docs/configuration/#cache-dir) value by editing the poetry config.
+Additionally, you can use the [`virtualenvs.in-project`](/docs/configuration/#virtualenvs.in-project) configuration variable
+to create virtual environment within your project directory.
+
+
+There are several ways to run commands within this virtual environment.
+
+
+### Using `poetry run`
+
+To run your script simply use `poetry run python your_script.py`.
+Likewise if you have command line tools such as `pytest` or `black` you can run them using `poetry run pytest`.
+
+### Activating the virtual environment
+
+The easiest way to activate the virtual environment is to create a new shell with `poetry shell`.
+To deactivate the virtual environment and exit this new shell type `exit`.
+To deactivate the virtual environment without leaving the shell use `deactivate`.
+
+!!!note
+
+	**Why a new shell?**
+	Child processes inherit their environment from their parents, but do not share
+	them. As such, any modifications made by a child process, is not persisted after
+	the child process exits. A Python application (Poetry), being a child process,
+	cannot modify the environment of the shell that it has been called from such
+	that an activated virtual environment remains active after the Poetry command
+	has completed execution.
+
+	Therefore, Poetry has to create a sub-shell with the virtual envrionment activated
+	in order for the subsequent commands to run from within the virtual environment.
+
+
+Alternatively, to avoid creating a new shell, you can manually activate the
+virtual environment by running `source {path_to_venv}/bin/activate` (`source {path_to_venv}\Scripts\activate.bat` on Windows).
+To get the path to your virtual environment run `poetry env info --path`.
+You can also combine these into a nice one-liner, `source $(poetry env info --path)/bin/activate`
+To deactivate this virtual environment simply use `deactivate`.
+
+|                   | POSIX Shell                                      | Windows                                     | Exit/Deactivate |
+|-------------------|------------------------------------------------|---------------------------------------------|-----------------|
+| New Shell         | `poetry shell`                                 | `poetry shell`                              | `exit`          |
+| Manual Activation | `source {path_to_venv}/bin/activate`           | `source {path_to_venv}\Scripts\activate.bat`| `deactivate`    |
+| One-liner         | ```source`poetry env info --path`/bin/activate```|                                             | `deactivate`    |
+
+
 ### Version constraints
 
 In our example, we are requesting the `pendulum` package with the version constraint `^1.4`.