Fix wrong extension in the install.txt

[prestancedesign]

Questions	Answers
Branch?	develop
Description?	Wrong filename : index.html must be index.php
Type?	bug fix
Category?	IN
BC breaks?	no
Deprecations?	no

Important guidelines

• Make sure your local branch is up to date before commiting your changes!
• Your code MUST respect our Coding Standards (for code written in PHP, JavaScript, HTML/CSS/Smarty/Twig, SQL)!
• Your commit name MUST respect our naming convention!

[maximebiloe]

Hi!

Your pull request description seems to be incomplete or malformed:

The description shouldn't be empty.
The type should be one of: new feature, improvement, bug fix, refacto.
The category should be one of: FO, BO, CO, IN, TE, WS, LO
Would you mind completing the contribution table ? This would help us understand how interesting your contribution is.

I just added back the table, please fill it.

Thank you!

[prestancedesign]

Hi!

Done !

First I had filled the table and then changed because for me I found that no categories corresponded to a typing error (wrong filename).

[maximebiloe]

Thank you @prestancedesign!