Add review guidance

dev.md

@@ -85,6 +85,46 @@ JupyterLab Desktop bundles JupyterLab front-end and a conda environment as Jupyt
 
   Application Installer will be created in `dist/JupyterLab.dmg` (macOS), `dist/JupyterLab.deb` (Debian, Ubuntu), `dist/JupyterLab.rpm` (Red Hat, Fedora) and `dist/JupyterLab-Setup.exe` (Windows) based on the platform
 
+## Review guidance
+
+Expected manual testing coverage depends on the PR, when pulling:
+
+- patch releases of JupyterLab or Electron: Testing on a single OS is sufficient.
+- minor or major JupyterLab releases and minor Electron releases: Test on multiple OSes.
+- major Electron releases: Test on all OSes.
+
+A release PR must be approved by at least two people.
+
+### Key Checks
+
+Depending on the PR, different part of the application may require testing. Use the guide below, but exercise your own judgment to skip or add more checks depending on circumstances.
+
+For patch dependency update PRs:
+
+- [ ] Notebooks UI launches (smoke test, no extensive testing required)
+
+For minor and major JupyterLab update PRs:
+
+- [ ] JupyterLab Desktop theme switching works
+- [ ] UI Mode switching works
+
+For conda update PRs:
+
+- [ ] Creating new environments from "Manage Python Environments" dialog works
+- [ ] The environment picker popover shows up with a list of environments
+- [ ] Switching environments works
+
+For minor and major Electron updates PR:
+
+- [ ] All checks listed above
+- [ ] No new errors in log files (e.g. `~/Library/Logs/jupyterlab-desktop/main.log`) and when launching from terminal with `jlab`
+- [ ] The welcome screen opens, displays the news feed, recent sessions, and allows to create new sessions
+- [ ] The settings window opens
+
+Before JupyterLab Desktop release:
+
+- [ ] All checks listed above
+
 ## Release Instructions
 
 For instructions on updating bundled JupyterLab packages and cutting a new release, please follow [Release.md](Release.md) document.