Recommend playground in issue template (#1021)

Author: loilo

.github/ISSUE_TEMPLATE/formatting.md

@@ -18,6 +18,12 @@ BEFORE SUBMITTING AN ISSUE:
     This means we have a very high bar for adding new options.
     Find out more: https://prettier.io/docs/en/option-philosophy.html
 
+Tip! Don't write this stuff manually.
+
+1. Go to https://loilo.github.io/prettier-php-playground/
+2. Paste your code and set options
+3. Press the "Report issue" button in the lower right
+
 -->
 
 **Prettier 1.16.4**