Add more details to the maintenance doc

MAINTENANCE.md

@@ -1,7 +1,22 @@
 ## Current state
 
+The state of cpp11 is pretty stable, it seems to have the features we need for most of our projects using C++.
+
 ## Known outstanding issues
 
+### Running the cpp11test tests
+
+Most of the test suite is in a sub-package, cpp11test.
+Probably the best way to run these tests is to install the development version of cpp11 and then run `devtools::test()` to run the cpp11test test suite.
+
+If tests failures occur the output from Catch isn't always easy to interpret.
+I have a branch of testthat https://github.com/jimhester/testthat/tree/catch-detailed-output that should make things easier to understand.
+I contributed those changes to the main testthat, but something changed after merging the more detailed output was lost, I unfortunately never had the time to track down the cause and fix it.
+
+In addition getting a debugger to catch when errors happen can be fiddly when running the cpp11test tests, something about the way that Catch redirects stderr / stdout interacts with the debugger.
+
+The GitHub Actions workflow has some additional logic to handle running the cpp11 tests https://github.com/r-lib/cpp11/blob/fd8ef97d006db847f7f17166cf52e1e0383b2d35/.github/workflows/R-CMD-check.yaml#L95-L102, https://github.com/r-lib/cpp11/blob/fd8ef97d006db847f7f17166cf52e1e0383b2d35/.github/workflows/R-CMD-check.yaml#L117-L124.
+
 ### False positive URL checks for git repositories in the vignettes
 
 If you run `urlchecker::url_check()` on the repo you will see the following false positives.
@@ -26,3 +41,9 @@ These only happen with the urlchecker package, they can be safely ignored and th
 If you forget to set `CPP_EVAL = "true"` then the vignette chunks will not run properly and the vignettes will not be rendered properly.
 
 ## Future directions
+
+Some work could be spent in smoothing out the `cpp_source()` / knitr chunk experience.
+Our main focus and use cases were in R packages, so that usage is more tested.
+Because we don't typically use cpp11 in non package contexts those use cases may not be as nice.
+
+For similar reasons the matrix support might be somewhat lacking, as the majority of our use cases do not deal with numeric matrices.