Add CONTRIBUTING.md with release process

Author: Jean85

CONTRIBUTING.md

@@ -0,0 +1,58 @@
+# Contribution notes
+
+## Release process
+
+ * Make sure `CHANGELOG.md` is up to date (add the release date) and the build is green.
+ * If this is the first release for this minor version, create a new branch for it:
+```
+    $ git checkout -b releases/1.7.x
+```
+ * Update the hardcoded `SentryBundle::VERSION` constant:
+```
+class SentryBundle extends Bundle
+{
+    const VERSION = '1.7.0';
+}
+```
+ * Commit the changes:
+```
+$ git commit -am "Release 1.7.0"
+```
+ * Tag the new commit:
+```
+git tag 1.7.0
+```
+ * Push the tag:
+```
+git push --tags
+```
+ * Switch back to `master`:
+```
+git checkout master
+```
+ * Add the next minor release to the `CHANGES` file:
+```
+## 1.8.0 (unreleased)
+```
+ * Update the hardcoded `SentryBundle::VERSION` constant:
+```
+class Raven_Client
+{
+    const VERSION = '1.8.x-dev';
+}
+```
+ * Lastly, update the composer version in ``composer.json``:
+
+```
+    "extra": {
+        "branch-alias": {
+            "dev-master": "1.8.x-dev"
+        }
+    }
+```
+ * Commit the changes:
+```
+$ git commit -am "Cleanup after release 1.7"
+```
+
+All done! Composer will pick up the tag and configuration automatically.