Added documentation page and reworked docs instructions to address jekyll issue #6586

Added a documentation page to track older versions rather than clutter
the homepage.

Jekyll seems to have bugs in it's exclude/keep_files feature. As such I
moved the doc directory to a different staging name.

README.md

@@ -13,7 +13,7 @@ and `sudo pip install Pygments`. See the Jekyll installation page for more detai
 You can generate the static ZooKeeper website by running:
 
 1. `jekyll build` in this directory.
-1. `cp -rp doc _site/.` - this will include the documentation (see "sub-dir" section below) in the generated site.
+1. `cp -rp _released_docs _site/doc` - this will include the documentation (see "sub-dir" section below) in the generated site.
 
 At this point the contents of _site are "staged" and can be reviewed prior to updating the ZooKeeper
 production website.
@@ -26,11 +26,11 @@ jekyll can serve the site via a web server. To build the site and run a web serv
 
 ## Docs sub-dir
 
-The product docs are not generated as part of the website. They are built separately for each release 
+The product documentation is not generated as part of the website. They are built separately for each release 
 of ZooKeeper from the ZooKeeper source repository.
 
 Typically during a release the versioned documentation will be recreated and should be copied, and committed,
-under the "doc" directory here.
+under the "_released_docs" directory here.
 
 
 ## Pygments

_config.yml

@@ -9,6 +9,3 @@ permalink: none
 
 exclude:
     - README.md
-    - doc
-keep_files:
-    - doc

_includes/sidenav.md

@@ -15,6 +15,7 @@
 
 * [Release 3.5.3-beta](doc/r3.5.3-beta)
 * [Release 3.4.11](doc/r3.4.11)
+* [Older Versions](documentation.html)
 
 ### Developers