Site building docs updated

Author: elizarov

RELEASE.md

@@ -53,7 +53,8 @@ To release new `<version>` of `kotlinx-coroutines`:
    * Create a release named `<version>`. 
    * Cut & paste lines from [`CHANGES.md`](CHANGES.md) into description.    
 
-3. Build and publish documentation for web-site: <br>
+3. Build and publish documentation for web-site
+   (make sure you have [Docker](https://www.docker.com/) installed first): <br>
    `site/deploy.sh <version> push`
 
 4. In [Bintray](https://bintray.com/kotlin/kotlinx/kotlinx.coroutines) admin interface:

site/README.md

@@ -2,13 +2,14 @@
 
 This module builds references documentation.
 
-## Building
-
-* Install [Jekyll](https://jekyllrb.com)
-* If you already have Ruby/Jekyll installed you might need to update its version:
-  * `cd site/docs`
-  * `bundle install`
-* In project root directory do:
-  * Run `./gradlew site`
-* The result is in `site/build/gh-pages/_site`
-* Upload it to github pages (`gh-pages` branch) 
+## Building docs
+
+* Install [Docker](https://www.docker.com/)
+* In the project root directory run `./gradlew site`
+* The resulting HTML pages are generated in `site/build/dist`
+* For continuous testing of the documentation run `./gradlew serve` and navigate
+  to the URL that is printed on the screen
+  * Update the docs via `./gradlew copyDocs` while `serve` is running
+
+For release use [`deploy.sh`](deploy.sh) that performs clean build of the site and pushes the results
+into `gh-pages` branch of the project.