made changes to installation and landing pages (#445)

* initial commit of changes to the installation and landing pages

* deleted original install; fixed the toc; fixed typos

* fixed some wording issues; fixed some formatting issues

* adding back install.rst to try to fix the conflict

---------

Co-authored-by: Aryan Salmanpour <aryan.salmanpour@amd.com>

[ROCm/rocdecode commit: 6cc30f12a4]

projects/rocdecode/docs/install/rocDecode-package-install.rst

@@ -0,0 +1,67 @@
+.. meta::
+  :description: Installing rocDecode with the package installer
+  :keywords: install, rocDecode, AMD, ROCm, basic, development, package
+
+********************************************************************
+Installing rocDecode with the package installer
+********************************************************************
+
+Three rocDecode packages are available:
+
+* ``rocdecode``: The rocDecode runtime package. This is the basic rocDecode package. It must always be installed.
+* ``rocdecode-dev``: The rocDecode development package. This package installs a full suite of libraries, header files, and samples. This package needs to be installed to use the rocDecode samples.
+* ``rocdecode-test``: A test package that provides a CTest to verify the installation. This package needs to be installed to use the rocDecode samples.
+
+All the required prerequisites are installed when the package installation method is used.
+
+
+Basic installation
+========================================
+
+Use the following commands to install only the rocDecode runtime package:
+
+.. tab-set::
+ 
+  .. tab-item:: Ubuntu
+
+    .. code:: shell
+
+      sudo apt install rocdecode
+
+  .. tab-item:: RHEL
+
+    .. code:: shell
+
+      sudo yum install rocdecode
+
+  .. tab-item:: SLES
+
+    .. code:: shell
+
+      sudo zypper install rocdecode
+
+
+Complete installation
+========================================
+
+Use the following commands to install ``rocdecode``, ``rocdecode-dev``, and ``rocdecode-test``:
+
+.. tab-set::
+
+  .. tab-item:: Ubuntu
+
+    .. code:: shell
+
+      sudo apt install rocdecode rocdecode-dev rocdecode-test
+
+  .. tab-item:: RHEL
+
+    .. code:: shell
+
+      sudo yum install rocdecode rocdecode-devel rocdecode-test
+
+  .. tab-item:: SLES
+
+    .. code:: shell
+
+      sudo zypper install rocdecode rocdecode-devel rocdecode-test