Update README and pyproject.toml.

I had meant to squash this into my original CL, but apparently forgot
to do that before it merged.

The README changes are just elaboration. The pyproject.toml changes
remove things that are not used.

Test: make check
Bug: None
Change-Id: Id47e2a8dcbf15ccb2f228652e7d7f0335d637309

README.md

diff --git a/README.md b/README.md
index 3fba691..11d0ca4 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,9 @@
 
 The development environment is managed using
 [Poetry](https://python-poetry.org/). If you need to make a non-trivial change
-you will want to install that so you can run the linters and formatters.
+you will want to install that so you can run the linters, formatters, and tests.
+Once installed, run `poetry install` in this directory to install the
+development dependencies.
 
 Run the type checker and linter with `make lint`.
 

pyproject.toml

diff --git a/pyproject.toml b/pyproject.toml
index fa15951..ccadcce 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,9 +26,7 @@
 fail_under = 100
 
 [tool.pytest.ini_options]
-addopts = "--strict-markers"
 asyncio_mode = "auto"
-markers = ["requires_network: marks a test that requires network access"]
 xfail_strict = true
 
 [tool.mypy]