Create FEATURES.md

Full list of features

FEATURES.md

+- Self Host
+  - Docker  
+  - Multiple Deployment Options (Heroku, Digital Ocean, Sandstorm, etc.)  
+- OAuth
+  - SAML
+  - LDAP
+  - CAS
+  - Facebook, Github, Google, etc.
+- I18N: More than 30 languages so far
+- File Uploading
+  - Upload to file system
+  - AWS + CDN
+- Live chat
+  - SMS Integration
+- Rich Media
+  - Audio Calls
+  - Video Conferencing
+  - Screensharing
+- Notifications
+  - Desktop and Mobile
+  - Use your own gateway
+- Apps
+  - Mobile
+  - Native
+- Integrations
+  - Hubot
+  - Incoming / Outgoing Webhooks
+  - Data Importer
+    - Import from Slack
+    - Import from Hipchat
+  - Slack Bridge
+- Profiles
+  - Custom avatars
+- Text Decorations
+  - Mentions
+  - Link Preview
+  - Markdown
+  - TexMath
+  - Emojis
+    - Reactions
+- History
+  - Search
+    - Full-text search
+    - Regex search
+- REST Api
+- Roles and Permissions
+- Off-the-record conversations
+- Slashcommands