[README] Add deploy button to Heroku (#1150)

* Add deploy button to Heroku
* Add composer.json and composer.lock (required by Heroku)

README.md

@@ -86,6 +86,7 @@ Thanks to the community, hosting your own instance of RSS-Bridge is as easy as c
 
 [![Deploy on Scalingo](https://cdn.scalingo.com/deploy/button.svg)](https://my.scalingo.com/deploy?source=https://github.com/sebsauvage/rss-bridge)
 [![Deploy to Docker Cloud](https://files.cloud.docker.com/images/deploy-to-dockercloud.svg)](https://cloud.docker.com/stack/deploy/?repo=https://github.com/rss-bridge/rss-bridge)
+[![Deploy to Heroku](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy)
 
 Getting involved
 ===

app.json

@@ -0,0 +1,8 @@
+{
+  "service": "Heroku",
+  "name": "RSS-Bridge",
+  "description": "RSS-Bridge is a PHP project capable of generating RSS and Atom feeds for websites which don't have one.",
+  "repository": "https://github.com/RSS-Bridge/rss-bridge",
+  "keywords": ["php", "rss-bridge", "rss"]
+}
+

composer.json

@@ -0,0 +1,12 @@
+{
+    "require": {
+	"php": ">=5.6",
+	"ext-mbstring": "*",
+	"ext-sqlite3": "*",
+	"ext-curl": "*",
+	"ext-openssl": "*",
+	"ext-libxml": "*",
+	"ext-simplexml": "*",
+	"ext-json": "*"
+    }
+}

composer.lock

@@ -0,0 +1,26 @@
+{
+    "_readme": [
+        "This file locks the dependencies of your project to a known state",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "This file is @generated automatically"
+    ],
+    "content-hash": "ef341ee18f28c7bd5832e188fe157734",
+    "packages": [],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": {
+        "php": ">=5.6",
+        "ext-mbstring": "*",
+        "ext-sqlite3": "*",
+        "ext-curl": "*",
+        "ext-openssl": "*",
+        "ext-libxml": "*",
+        "ext-simplexml": "*",
+        "ext-json": "*"
+    },
+    "platform-dev": []
+}