Add more detailed project overview

README.md

@@ -3,4 +3,60 @@
 A [Tox](https://tox.readthedocs.io/en/latest/) plugin for installing Tox environment
 dependencies using [Poetry](https://python-poetry.org/) from the Poetry lockfile.
 
-Very early prototype, still under development
+⚠️ **This project is a very, very early prototype and should not be used in any production
+capacity.**
+
+
+## Why would I use this?
+
+[The point of using a lockfile is to create reproducable builds](https://docs.gradle.org/current/userguide/dependency_locking.html). One of the main points of Tox is to [allow a Python
+package to be built and tested in multiple environments](https://tox.readthedocs.io/en/latest/#what-is-tox). However, in the Tox configuration file the dependencies are specified with
+standard dynamic ranges and passed directly to Pip. This means that the reproducability
+a lockfile brings to a project is circumvented when running the tests.
+
+The obvious solution to this problem is to add the dependencies required for testing to the
+lockfile as development dependencies so that they are locked along with the primary dependencies
+of the project. The only remaining question however, is how to install the dev-dependencies from
+the lockfile into the Tox environment when Tox sets it up. [For very good reason](https://dev.to/elabftw/stop-using-sudo-pip-install-52mn) Tox uses independent
+[virtual environments](https://docs.python.org/3/tutorial/venv.html) for each environment a
+project defines, so there needs to be a way to install a locked dependency into a Tox
+environment.
+
+This is where this plugin comes in.
+
+Traditionally Tox environments specify dependencies and their corresponding versions inline in
+[PEP-440](https://www.python.org/dev/peps/pep-0440/) format like below:
+
+```ini
+[testenv]
+description = Run the tests
+deps =
+  foo == 1.2.3
+  bar >=1.3,<2.0
+  baz
+```
+
+This runs into the problem outlined above: many different versions of the `bar` dependency
+could be installed depending on what the latest version is that matches the defined range. The
+`baz` dependency is entirely unpinned making it a true wildcard, and even the seemingly static
+`foo` dependency could result in subtly different files being downloaded depending on what's
+available in the upstream mirrors.
+
+However these same versions, specified in the [pyproject.toml](https://snarky.ca/what-the-heck-is-pyproject-toml/) file, result in reproducible
+installations when using `poetry install` because they each have a specific version and file
+hash specified in the lockfile. The versions specified in the lockfile are updated only when
+`poetry update` is run.
+
+This plugin allows environment dependencies to be specified in the [tox.ini](https://tox.readthedocs.io/en/latest/config.html) configuration file
+just by name. The package is automatically retrieved from the lockfile and the Poetry backend
+is used to install the singular locked package version to the Tox environment. When the
+lockfile is updated, the Tox environment will automatically install the newly locked package
+as well. All dependency requirements are specified in one place (pyproject.toml), all
+dependencies have a locked version, and everything is installed from that source of truth.
+
+
+## Planned features
+
+* Per-environment disabling (i.e. fallback to the default Tox installation backend)
+* Detection of lockfile changes that trigger Tox environment recreation
+* Tests