Added Selenide (Open Source Selenium Java Library) with description to Ecosystem

[vinogradoff]

Types of changes

• Change to the site (I am attaching a screenshot showing the before and after, if needed)

CLA

• By placing an X in the preceding checkbox, I verify that I have signed the [Contributor License Agreement]

[diemol]

This PR did not have any effect, the change was not deployed, please read the contribution guidelines, for more details check this comment.
With the difference that the file to change is https://github.com/SeleniumHQ/seleniumhq.github.io/blob/master/site_source_files/themes/selenium/layouts/thirdparty/section.html, where open source non profit projects are placed (we will do some changes about it soon).

[vinogradoff]

Sorry Diego, my bad.