Change "Follow us on Twitter" text to "Follow us on X"

[NayanshiSingh]

Describe the bug:
The text "Follow us on Twitter" on the home page should be updated to "Follow us on X" to reflect the new branding.

To Reproduce:
Steps to reproduce the behavior:

1. Go to the home page.
2. Locate the "Follow us on Twitter" text.

Expected behavior:
The text should read "Follow us on X" instead of "Follow us on Twitter."

Screenshots:

[vfdev-5]

The source of that page is here: https://github.com/pytorch-ignite/pytorch-ignite.ai/blob/2d5485a18bb152ceafe192f7d9ed87c382e9d871/themes/ignite/layouts/index.html#L164-L165

[NayanshiSingh]

@vfdev-5 I have raised the PR pytorch-ignite/pytorch-ignite.ai#204
on pytorch-ignite.ai

[vfdev-5]

We can keep old name "Twitter" for now