docs: add info about build workarounds

Add info about #301 and #299

README.md

@@ -88,6 +88,16 @@ the [production branch](https://github.com/NebraLtd/helium-miner-software/tree/p
 
 Do note that the Docker Tag is hard coded in the `docker-compose.yml` file.
 
+## Balena deploy builds
+
+Whilst in theory you can run matrix builds to build to several balena fleets simultaneously using GitHub Actions we found (at the time of writing - December 2021) that this did not perform satisfactorily in practice. We deploy on a production release now to 16 separate fleets meaning 16 separate builds triggered via the balena API simultaneously. Somewhere between 50 and 100% of the builds would fail each time.
+
+We have discovered a useful fix for this using the following two workarounds:
+- use [multiple API keys](https://github.com/NebraLtd/helium-miner-software/pull/301) within the action to avoid any rate limiting or timeout issues.
+- add random periods of delay to each matrix action run using using a [random sleep on the command line](https://github.com/NebraLtd/helium-miner-software/pull/300) within the action.
+
+This has allowed our builds to continue deploying successfully.
+
 ## Dealing with failed builds
 
 On occasion (as originally described [in this issue](https://github.com/NebraLtd/helium-miner-software/issues/293)) CI/CD builds via GitHub actions will fail to push correctly to balena. We have found that as a workaround, it is often possible to force push these to balena as draft releases using the `--draft` tag in the `balena deploy` command of the balena CLI tool. For example: