Fix typos discovered by codespell

Author: cclauss

README.md

@@ -72,10 +72,10 @@ those fixtures are shared between threads.
        adding support for Python 3.14 to a library that already
        runs tests under pytest-run-parallel on Python 3.13 or
        older.
-    - `--mark-hypothesis-as-unsafe` to always skip runing tests that
+    - `--mark-hypothesis-as-unsafe` to always skip running tests that
       use [hypothesis](https://github.com/hypothesisworks/hypothesis).
-      While newer version of Hypothesis are thread-safe, and versions
-      which are not are automatically skipped by `pytest-run-parallel`,
+      While newer versions of Hypothesis are thread-safe, and versions
+      which are not automatically skipped by `pytest-run-parallel`,
       this flag is an escape hatch in case you run into thread-safety
       problems caused by Hypothesis, or in tests that happen to use
       hypothesis and were skipped in older versions of pytest-run-parallel.
@@ -134,7 +134,7 @@ back to running all tests single-threaded.
 ## Requirements
 
 `pytest-run-parallel` depends exclusively on `pytest`. Optionally
-intalling `psutil` will help with identifying the number of logical
+installing `psutil` will help with identifying the number of logical
 cores available to the testing process in systems where that's not
 possible with the Python stdlib.
 
@@ -278,7 +278,7 @@ def test_fixture(my_fixture, arg):
     ...
 ```
 
-Both modes of operations are supported simultaneously, i.e.,
+Both modes of operation are supported simultaneously, i.e.,
 
 ```bash
 # test_something_1 and test_fixture will be run using their set number of
@@ -294,7 +294,7 @@ Sanitizer](https://clang.llvm.org/docs/ThreadSanitizer.html). Setting
 sanitizer cannot detect races because the test is not parallelized.
 
 Older versions of pytest-run-parallel always marked tests using the `warnings`
-and `ctypes` modules as thread-unsafe, since both were not thread-safe until
+and `ctypes` modules as thread-unsafe, since neither was thread-safe until
 Python 3.14. If you are adding support for Python 3.14 and would like to
 continue marking tests that use `warnings` or `ctypes`, pass
 `--mark-warnings-as-unsafe` or `--mark-ctypes-as-unsafe`, respectively, in your
@@ -315,7 +315,7 @@ def test_skip_if_parallel(num_parallel_threads):
     ...
 ```
 
-The `thread_index` and `iteration_index` fixtures are also avaliable, which enable
+The `thread_index` and `iteration_index` fixtures are also available, which enable
 tests to display different behavior between threads and iterations.
 
 ```python