Update README with dependencies

codecs/README.md

@@ -4,7 +4,7 @@ This folder contains a self-contained sub-project for each encoder and decoder t
 
 ## Build
 
-Each subproject can be built using the following commands:
+Each subproject can be built using [Docker](https://www.docker.com/) the following commands:
 
 ```
 $ npm install

codecs/mozjpeg_enc/README.md

@@ -3,6 +3,12 @@
 - Source: <https://github.com/mozilla/mozjpeg>
 - Version: v3.3.1
 
+## Dependencies
+
+- Docker
+- Automake
+- pkg-config
+
 ## Example
 
 See `example.html`

codecs/webp_enc/README.md

@@ -3,6 +3,10 @@
 - Source: <https://github.com/webmproject/libwebp>
 - Version: v0.6.1
 
+## Dependencies
+
+- Docker
+
 ## Example
 
 See `example.html`