Update R2 directory name

- Update the R2 directory from 'current' to 'r2_release' in: build guides,
  install guides. This will enable persistent URLs for each release.
- Minor edit to remove reference to versioned content in developer resources
  (there is no versioned content for developer resources)

Change-Id: I336117a12a2c103e9e16739e3a8fed1d1d83683d
Signed-off-by: Kristal Dale <kristal.dale@intel.com>

doc/source/contributor/index.rst

@@ -39,7 +39,7 @@ guides for StarlingX are release-specific).
 .. toctree::
    :maxdepth: 1
 
-   build_guides/current/index
+   build_guides/r2_release/index
    build_guides/r1_release/index
 
 --------------------

doc/source/deploy_install_guides/index.rst

@@ -15,7 +15,7 @@ StarlingX R2.0 is the latest officially released version of StarlingX.
 .. toctree::
    :maxdepth: 1
 
-   current/index
+   r2_release/index
 
 ---------------------
 Upcoming R3.0 release

doc/source/deploy_install_guides/r1_release/index.rst

@@ -242,7 +242,7 @@ Unload firewall and disable firewall on boot:
 Getting the StarlingX ISO image
 -------------------------------
 
-Follow the instructions from the :doc:`/contributor/build_guides/current/index` to build a
+Follow the instructions from the :doc:`/contributor/build_guides/r1_release/index` to build a
 StarlingX ISO image.
 
 **********

doc/source/developer_resources/index.rst

@@ -4,13 +4,9 @@
 Developer Resources
 ===================
 
-StarlingX developer resources exist that help you understand the
+StarlingX developer resources provide information to help you understand the
 architecture of the documentation, how to navigate the StarlingX
-source code, and understand the development process.
+source code, and to understand the development process.
-
-The developer guide is release-specific.
-The following list provides help on choosing the correct
-developer guide based on a release:
 
 .. toctree::
    :maxdepth: 1