Fundraising tech/notes/Draft:Documentation overhaul

Brainstorming: topics to include

 * FR-Tech source repositories and codebases, what they're used for, where they're deployed, how they're used, links to related documentation pages, links to upstream repos (if applicable)
 * Civicrm: Triggers: What they're for, how to update, how they work for adding fields, how to test, how they're deployed on production and locally
 * Composer: How we run it locally, on production and in CI, and why, and troubleshooting tips
 * Process-control
 * Deploymet: Steps for all service in the FR stack and config changes
 * Integrations: Adyen Checkout: Explanation of flow for different payment options (cc, cc with 3DS, rtbt), including pointers to codebases and methods responsible for each step, and UML interaction diagrams
 * DonationInterface: Overview of main classes and methods and their functions in the system