Recommend poetry in docs (#12475)

* Recommend poetry in docs

- readme
- contributor guide
- upgrade notes
- new dev cheat sheet for poetry

Co-authored-by: Shay <hillerys@element.io>
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

docs/development/contributing_guide.md

@@ -48,19 +48,28 @@ can find many good git tutorials on the web.
 
 # 4. Install the dependencies
 
-Once you have installed Python 3 and added the source, please open a terminal and
-setup a *virtualenv*, as follows:
+Synapse uses the [poetry](https://python-poetry.org/) project to manage its dependencies
+and development environment. Once you have installed Python 3 and added the
+source, you should install `poetry`.
+Of their installation methods, we recommend
+[installing `poetry` using `pipx`](https://python-poetry.org/docs/#installing-with-pipx),
+
+```shell
+pip install --user pipx
+pipx install poetry
+```
+
+but see poetry's [installation instructions](https://python-poetry.org/docs/#installation)
+for other installation methods.
+
+Next, open a terminal and install dependencies as follows:
 
 ```sh
 cd path/where/you/have/cloned/the/repository
-python3 -m venv ./env
-source ./env/bin/activate
-pip install wheel
-pip install -e ".[all,dev]"
-pip install tox
+poetry install --extras all
 ```
 
-This will install the developer dependencies for the project.
+This will install the runtime and developer dependencies for the project.
 
 
 # 5. Get in touch.
@@ -117,11 +126,10 @@ The linters look at your code and do two things:
 - ensure that your code follows the coding style adopted by the project;
 - catch a number of errors in your code.
 
-The linter takes no time at all to run as soon as you've [downloaded the dependencies into your python virtual environment](#4-install-the-dependencies).
+The linter takes no time at all to run as soon as you've [downloaded the dependencies](#4-install-the-dependencies).
 
 ```sh
-source ./env/bin/activate
-./scripts-dev/lint.sh
+poetry run ./scripts-dev/lint.sh
 ```
 
 Note that this script *will modify your files* to fix styling errors.
@@ -131,15 +139,13 @@ If you wish to restrict the linters to only the files changed since the last com
 (much faster!), you can instead run:
 
 ```sh
-source ./env/bin/activate
-./scripts-dev/lint.sh -d
+poetry run ./scripts-dev/lint.sh -d
 ```
 
 Or if you know exactly which files you wish to lint, you can instead run:
 
 ```sh
-source ./env/bin/activate
-./scripts-dev/lint.sh path/to/file1.py path/to/file2.py path/to/folder
+poetry run ./scripts-dev/lint.sh path/to/file1.py path/to/file2.py path/to/folder
 ```
 
 ## Run the unit tests (Twisted trial).
@@ -148,16 +154,14 @@ The unit tests run parts of Synapse, including your changes, to see if anything
 was broken. They are slower than the linters but will typically catch more errors.
 
 ```sh
-source ./env/bin/activate
-trial tests
+poetry run trial tests
 ```
 
 If you wish to only run *some* unit tests, you may specify
 another module instead of `tests` - or a test class or a method:
 
 ```sh
-source ./env/bin/activate
-trial tests.rest.admin.test_room tests.handlers.test_admin.ExfiltrateData.test_invite
+poetry run trial tests.rest.admin.test_room tests.handlers.test_admin.ExfiltrateData.test_invite
 ```
 
 If your tests fail, you may wish to look at the logs (the default log level is `ERROR`):
@@ -169,7 +173,7 @@ less _trial_temp/test.log
 To increase the log level for the tests, set `SYNAPSE_TEST_LOG_LEVEL`:
 
 ```sh
-SYNAPSE_TEST_LOG_LEVEL=DEBUG trial tests
+SYNAPSE_TEST_LOG_LEVEL=DEBUG poetry run trial tests
 ```
 
 By default, tests will use an in-memory SQLite database for test data. For additional
@@ -180,7 +184,7 @@ database state to be stored in a file named `test.db` under the trial process'
 working directory. Typically, this ends up being `_trial_temp/test.db`. For example:
 
 ```sh
-SYNAPSE_TEST_PERSIST_SQLITE_DB=1 trial tests
+SYNAPSE_TEST_PERSIST_SQLITE_DB=1 poetry run trial tests
 ```
 
 The database file can then be inspected with: