Document troublehsooting step for non-full erlang install (#219)

Fixes #208

Author: axelson

README.md

@@ -118,6 +118,15 @@ Basic troubleshooting steps:
 
 If your code doesn't compile in ElixirLS, it may be because ElixirLS compiles code with `MIX_ENV=test` (by default). So if you are missing some configuration in the test environment, your code may not compile.
 
+If you get an error like the following immediately on startup:
+
+```
+[Warn  - 1:56:04 PM] ** (exit) exited in: GenServer.call(ElixirLS.LanguageServer.JsonRpc, {:packet, %{...snip...}}, 5000)
+    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
+```
+
+and you installed Elixir and Erlang from the Erlang Solutions repository, you may not have a full installation of erlang. This can be solved with `sudo apt-get install esl-erlang`. Originally reported in [#208](https://github.com/elixir-lsp/elixir-ls/issues/208).
+
 ## Known Issues
 
 * `.exs` files don't return compilation errors