update find-image for denv and add useful CMake options

docs/src/custom-acts.md

@@ -36,3 +36,9 @@ we just need to build ldmx-sw with specific `cmake` options pointing it to our n
 just configure -DActs_DIR=/path/to/ldmx/acts/install
 just build
 ```
+Some other CMake options may be required depending on your version of ACTS and the version of the dev
+image you are using. Below are some options that we've come across while testing. They can be set on the
+the command line when running `just configure` with `-D<name>=<value>` like `Acts_DIR` above.
+- `CMAKE_FIND_DEBUG_MODE`: may need to be turned `OFF`
+- `nlohmann_json_DIR`: may need to be directed to the specific version that was installed with ACTS
+  - e.g. `-Dnlohmann_json_DIR=/path/to/ldmx/acts/install/lib/cmake/nlohmann_json/`

docs/src/image-version.md

@@ -39,4 +39,8 @@ variable `apptainer` defines at runtime.
 ```
 denv printenv APPTAINER_CONTAINER
 ```
+Putting all this together, we can find the image version label with the following one-liner.
+```
+apptainer inspect $(denv printenv APPTAINER_CONTAINER) | grep org.opencontainers.image.version
+```
 ~~~