Rewrite issue template to mention yarn/npm problems

Author: gaearon

.github/ISSUE_TEMPLATE.md

@@ -24,35 +24,44 @@
  You can find webpack docs at https://webpack.js.org/.
 -->
 
-
-### Can you also reproduce the problem with npm 4.x?
+### Did you try recovering your dependencies?
 
 <!--
- Many errors, especially related to "missing modules", are due to npm bugs.
- Which version of npm are you running? You can find out by checking:
-
- npm -v
+ Your module tree might be corrupted, and that might be causing the issues.
+ Let's try to recover it. First, delete these files and folders in your project:
 
- If it is 5.x, please be aware that it has more than 50 known bugs, and
- is not guaranteed to work with Create React App.
+ * node_modules
+ * package-lock.json
+ * yarn.lock
 
- If it's not starting with 4, try to install npm 4.x:
+ Then you need to decide which package manager you prefer to use.
+ We support both npm (https://npmjs.com) and yarn (http://yarnpkg.com/).
+ However, **they can't be used together in one project** so you need to pick one.
+ 
+ If you decided to use npm, run this in your project directory:
 
- npm install -g npm@4
- cd your_project_directory
- rm -rf node_modules
- npm cache clear
+ npm install -g npm@latest
  npm install
 
- Then try to reproduce the issue again.
- Can you still reproduce it?
+ This should fix your project.
+ 
+ If you decided to use yarn, update it first (https://yarnpkg.com/en/docs/install).
+ Then run in your project directory:
+
+ yarn
+
+ This should fix your project.
 
- Note: Please try this even if you are using Yarn so that we know whether it's a Yarn-only bug.
+ Importantly, **if you decided to use yarn, you should never run `npm install` in the project**.
+ For example, yarn users should run `yarn add <library>` instead of `npm install <library>`.
+ Otherwise your project will break again.
+
+ Have you done all these steps and still see the issue?
+ Please paste the output of `npm --version` and/or `yarn --version` to confirm.
 -->
 
 (Write your answer here.)
 
-
 ### Which terms did you search for in User Guide?
 
 <!--