add dev github action and update contributing guide (#77)

Signed-off-by: Gerald Shen <geshen@nvidia.com>

.github/workflows/sync_branch.yaml

@@ -0,0 +1,24 @@
+name: sync main with dev
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  sync-branches:
+    runs-on: ubuntu-latest
+    name: syncing main with dev
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up Node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+      - name: Opening pull request
+        id: pull
+        uses: tretuna/sync-branches@1.4.0
+        with:
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+          FROM_BRANCH: "main"
+          TO_BRANCH: "dev"

CONTRIBUTING.md

@@ -4,14 +4,18 @@ Thanks for the interest in contributing to NeMo-Aligner. We do all of NeMo-Align
 
 # Pull Requests (PR) Guidelines
 
-**Send your PRs to the `main` branch**
+**Send your PRs to the `main` or `dev` branch**
 
 1) Make sure your PR does one thing. Have a clear answer to "What does this PR do?".
 2) Read General Principles and style guide below
 3) Make sure you sign your commits. E.g. use ``git commit -sS`` when committing.
 4) Make sure all unittests finish successfully before sending PR ``pytest`` or (if your dev box does not have GPU) ``pytest --cpu`` from the root folder
 5) Send your PR and request a review
 
+**NOTE**: The `main` branch uses a fixed NeMo version which we will update on every release. The `dev` branch is the branch that has all commits from `main` but uses NeMo's main branch: this branch is less stable but we run nightly tests on it to make sure everything works. We only provide the dockerfile that works with `main`, which is the branch most PRs should target unless they require the latest NeMo main (in which case they should target `dev`).
+
+Every release `dev` and `main` will sync to be the same.
+
 ## Unit tests
 Quick unit tests (locally, while developing)
 ```