README: Add some troubleshooting info for compilation issues.

README.md

@@ -34,6 +34,16 @@ Currently Pleroma is not packaged by any OS/Distros, but if you want to package
 ### Docker
 While we don’t provide docker files, other people have written very good ones. Take a look at <https://github.com/angristan/docker-pleroma> or <https://glitch.sh/sn0w/pleroma-docker>.
 
+### Compilation Troubleshooting
+If you ever encounter compilation issues during the updating of Pleroma, you can try these commands and see if they fix things:
+
+- `mix deps.clean --all`
+- `mix local.rebar`
+- `mix local.hex`
+- `rm -r _build`
+
+If you are not developing Pleroma, it is better to use the OTP release, which comes with everything precompiled.
+
 ## Documentation
 - Latest Released revision: <https://docs.pleroma.social>
 - Latest Git revision: <https://docs-develop.pleroma.social>