Add note about dialyzer high CPU usage to readme and issue template. (#293)

* Add note about dialyzer high CPU usage to readme and issue template.

* Update .github/ISSUE_TEMPLATE.md

Co-authored-by: Łukasz Samson <lukaszsamson@gmail.com>

* Update .github/ISSUE_TEMPLATE.md

Co-authored-by: Łukasz Samson <lukaszsamson@gmail.com>

Author: axelson

.github/ISSUE_TEMPLATE.md

@@ -12,6 +12,8 @@
 - [ ] Stop your editor, remove the entire `.elixir_ls` directory, then restart your editor
   * NOTE: This will cause you to have to re-run the dialyzer build for your project
 
+If you're experiencing high CPU usage, it is most likely Dialyzer building the PLTs; after it's done the CPU usage should go back to normal. You could also disable Dialyzer in the settings.
+
 ### Logs
 
 1.  If using a client other than VS Code, please try VSCode's "ElixirLS: Elixir support and debugger" extension. Does it reproduce your failure?

README.md

@@ -24,6 +24,8 @@ The original repository has now been deprecated in favor of this one. Any IDE ex
 
 ![Screenshot](images/screenshot.png?raw=true)
 
+Note: On first run Dialyzer will build a PLT cache which will take a considerable amount of CPU time (usually 10+ minutes). After that is complete the CPU usage will go back to normal. Alternatively instead of waiting you can disable Dialyzer in the settings.
+
 ## Supported versions
 
 Elixir: