Add note about CI using temporary merge commits to the docs (#136)

docs/pages/devdocs/testing.dox

@@ -28,6 +28,21 @@
  *  cd <my_build_dir>
  *  ctest
  *  \endcode
+ *
+ * \subsection testing_github Automated tests on GitHub
+ *
+ * AqNWB uses GitHub Actions defined in the [.github/workflows](https://github.com/NeurodataWithoutBorders/aqnwb/tree/main/.github/workflows) 
+ * folder to automatically run all unit tests, spellchecks, linter, etc. on all pull requests.  
+ * 
+ * \note
+ * For pull requests, **GitHub Actions often checks out a temporary merge commit**. 
+ * This commit represents the state of the code as if the pull request were to be merged 
+ * into the target branch (usually ``main``). This allows the CI to test the combined code
+ * without actually merging it. These temporary merge commits are not part of the repository's
+ * history and exist only in the context of the CI job. That is, if you are experiencing errors
+ * in the CI but the indicated lines of code do not match the code in the PR, then this is 
+ * likely due the PR being out-of-sync with the target branch of the PR. 
+
  *
  * \section testing_spellcheck Spellcheck
  *