Add readme for steps on how to update fork (open-telemetry#9)

README.md

@@ -38,6 +38,30 @@
 </p>
 
 ---
+# Airbnb-specific fork of the open-telemetry/opentelemetry-collector-contrib OSS repo.
+
+As of 8/4/2022, changes are localized only to receiver/statsdreceiver.
+
+## To update the fork from upstream:
+Prerequisites:
+* Upstream set
+  * `git remote add upstream https://github.com/open-telemetry/opentelemetry-collector-contrib.git`
+* Local repo up to date
+  * `git fetch --all --prune --jobs=10`
+  * `git pull`
+
+Update fork:
+* Check out main `airbnb` branch
+  * `git checkout origin/airbnb`
+* Apply airbnb commits on top of new release
+  * `git rebase --onto <tag of new release> upstream/main`
+* Create new branch and push for review
+  * `git checkout -b <branch_name>`
+* Push branch and open for review. Gain a PR approval and passing CI
+* Force push commits from branch onto remote airbnb branch
+  * `git push --force origin <branch_name>:airbnb`
+
+--- 
 
 # OpenTelemetry Collector Contrib