Add instructions for troubleshooting ElixirLS (#5)

This adds some steps to fixing the problem with the plugin
not being able to start the language server.

Author: terenceponce

README.md

@@ -20,6 +20,30 @@ Elixir language server extension based on [elixir-ls](https://github.com/JakeBec
 - Smart closing of code blocks
 - Code formatter
 
+## Troubleshooting
+
+### Server fails to start
+
+If, for some reason, the language server fails to start, you can try doing a manual installation of [ElixirLS](https://github.com/JakeBecker/elixir-ls) to fix the problem.
+
+Start by building a binary of ElixirLS from its source:
+
+```
+git clone https://github.com/JakeBecker/elixir-ls.git ~/.elixir-ls
+cd ~/.elixir-ls
+mix deps.get && mix compile && mix elixir_ls.release -o release
+```
+
+Afterwards, create or update your ~/.vim/coc-settings.json file and add this line:
+
+```json
+{
+  "elixir.pathToElixirLS": "~/.elixir-ls/release/language_server.sh"
+}
+```
+
+Doing these steps should make this plugin work with [CoC](https://github.com/neoclide/coc.nvim).
+
 ## License
 
 MIT