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?
 
 <!--