Added a note about the side effects of enabling both PHP and Twig
Improved the explanation thanks to @stof comments
Reworded the explanation about the limitation of enablin PHP templates
minor #4220 Added a note about the side effects of enabling both PHP and Twig (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
----------

Added a note about the side effects of enabling both PHP and Twig

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3293

Commits
-------

fbbabb1 Reworded the explanation about the limitation of enablin PHP templates
5e47417 Improved the explanation thanks to @stof comments
3828162 Added a note about the side effects of enabling both PHP and Twig