chore: bootstrap module from working instance and add install guide

INSTALL.md

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+# Donations Installation Guide
+
+This guide installs the `donations` module in a reusable way for any HumHub instance.
+
+## 1. Requirements
+
+- HumHub `1.14+`
+- Module directory access on the target instance
+- A configured payment provider setup (Stripe and/or PayPal) after installation
+- Optional but recommended: `rescue_foundation` module
+
+## 2. Clone into HumHub Modules Directory
+
+The folder name must be exactly `donations`.
+
+```bash
+git clone https://gitea.kelinreij.duckdns.org/humhub-modules/donations.git \
+  /var/www/localhost/htdocs/protected/modules/donations
+```
+
+If the folder already exists:
+
+```bash
+cd /var/www/localhost/htdocs/protected/modules/donations
+git pull
+```
+
+## 3. Enable the Module
+
+In HumHub UI:
+
+1. Go to `Administration` -> `Modules`.
+2. Enable `Donations`.
+3. Enable it per space where donations should be active.
+
+## 4. Run Migrations
+
+From the HumHub app host/container:
+
+```bash
+php /var/www/localhost/htdocs/protected/yii migrate/up \
+  --include-module-migrations=1 --interactive=0
+```
+
+## 5. Post-Install Setup
+
+1. Open `Space` -> `Settings` -> `Donations`.
+2. Run module setup if prompted.
+3. Configure provider credentials and webhook values.
+4. Create at least one donation goal.
+
+## 6. Verify
+
+1. Open `Space` -> `Donations`.
+2. Submit a test donation intent.
+3. Confirm transaction records update as expected.
+
+## Docker Example
+
+```bash
+docker exec humhub php /var/www/localhost/htdocs/protected/yii migrate/up \
+  --include-module-migrations=1 --interactive=0
+```