Prep work for branch renaming (#389)

* Add `amd-staging` and `amd-mainline` to workflow.
* Update branch names in documentation
* Change `dev` to `amd-staging` and `main` to `amd-mainline` in documentation.
* Remove references from 2.x from workflows.
* Convert the link to LICENSE to a relative path in CONTRIBUTING.

---------

Signed-off-by: David Galiffi <David.Galiffi@amd.com>

.github/workflows/docs.yml

@@ -2,7 +2,7 @@ name: Documentation
 
 on:
   push:
-    branches: ["main"]
+    branches: [ main, amd-mainline ]
     paths:
       - 'docs/archive/docs-2.x/**'
       - 'docs/archive/docs-1.x/**'
@@ -36,7 +36,7 @@ jobs:
       - name: Build 1.x docs
         run: |
           cd docs/archive/docs-1.x
-          make html	
+          make html
       - name: Build 2.x docs
         run: |
           cd docs/archive/docs-2.x