Update .gitignore and install instructions

.gitignore

@@ -1,4 +1,9 @@
 /conf.php
+/dist/
+/node_modules/
+/npm-debug.log
 /vendor/
 /data/
 /composer.lock
+/yarn.lock
+*.swp

README.md

@@ -3,12 +3,14 @@
 git clone https://github.com/plepe/openstreetbrowser.git
 cd openstreetbrowser
 npm install
+composer install
 git submodule init
 git submodule update
 cp conf.php-dist conf.php
 nano conf.php
 npm run build
 modulekit/build_cache
+bin/download_dependencies
 ```
 
 ### Upgrade