Vendor composer.phar so install works on a fresh clone

- Un-ignore composer.phar (keep vendor/ and SQLite gitignored)
- Document install/bootstrap in README

README.md

@@ -59,12 +59,23 @@ cd RSS-Feed
 
 ### 2. Install dependencies
 
+`composer.phar` is committed with the repo, so no global Composer is required:
+
 ```bash
-php composer.phar install
+php composer.phar install --no-dev --optimize-autoloader
 ```
 
-This populates `vendor/`. If Composer is installed globally, `composer install`
-works the same. (`vendor/` and the SQLite DB are gitignored.)
+This populates `vendor/` (both `vendor/` and the SQLite DB are gitignored, so they
+are created here). A system Composer works the same:
+`composer install --no-dev --optimize-autoloader`.
+
+If `composer.phar` is ever missing, fetch it once:
+
+```bash
+php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+php composer-setup.php --install-dir=. --filename=composer.phar
+rm composer-setup.php
+```
 
 ### 3. Configure