README: remove confusing comments about poetry.

poetry is used as a build tool, but people who want to install and use
the package have no need to interact directly with poetry.  Moreover,
the "poetry install" command doesn't work.  Remove comments that
suggest otherwise.

(If people are already using poetry for reasons of their own, there's
nothing stopping them from adding wfdb as a dependency to their own
project.  In that case, they should know to consult the documentation
of the tools they're using.)

Also clarify that installing "dev" dependencies is an optional thing
for developers, and not a required installation step.

Author: Benjamin Moody

README.md

@@ -21,32 +21,26 @@ See the [demo.ipynb](https://github.com/MIT-LCP/wfdb-python/blob/main/demo.ipynb
 
 ## Installation
 
-The distribution is hosted on PyPI at: <https://pypi.python.org/pypi/wfdb/>. The package can be directly installed from PyPI using either pip or poetry:
+The distribution is hosted on PyPI at: <https://pypi.python.org/pypi/wfdb/>. The package can be directly installed from PyPI using pip:
 
 ```sh
 pip install wfdb
-poetry add wfdb
 ```
 
 On Linux systems, accessing _compressed_ WFDB signal files requires installing `libsndfile`, by running `sudo apt-get install libsndfile1` or `sudo yum install libsndfile`. Support for Apple M1 systems is a work in progess (see <https://github.com/bastibe/python-soundfile/issues/310> and <https://github.com/bastibe/python-soundfile/issues/325>).
 
 The development version is hosted at: <https://github.com/MIT-LCP/wfdb-python>. This repository also contains demo scripts and example data. To install the development version, clone or download the repository, navigate to the base directory, and run:
 
 ```sh
-# Without dev dependencies
 pip install .
-poetry install
+```
 
-# With dev dependencies
-pip install ".[dev]"
-poetry install -E dev
+If you intend to make changes to the repository, you can install additional packages that are useful for development by running:
 
-# Install the dependencies only
-poetry install -E dev --no-root
+```sh
+pip install ".[dev]"
 ```
 
-**See the [note](https://github.com/MIT-LCP/wfdb-python/blob/main/DEVELOPING.md#package-and-dependency-management) about dev dependencies.**
-
 ## Developing
 
 Please see the [DEVELOPING.md](https://github.com/MIT-LCP/wfdb-python/blob/main/DEVELOPING.md) document for contribution/development instructions.