Titles in List of Extensions are rendered as links

[BoHristova]

What happened:

• The entry pages in the List of Extensions sections have titles that are links.
• The links point to https://gardener.cloud.

What you expected to happen:

Titles should be plain text, not links.

How to reproduce it (as minimally and precisely as possible):

1. Go to https://gardener.cloud/docs/extensions/.
2. Open any extension entry page (e.g., Gardener Extension for Alicloud provider).
3. Observe that the page title is a hyperlink pointing to https://gardener.cloud.

Anything else we need to know:

The issue seem to be the source READMEs of the individual extension repositories. The top-level heading is written as a Markdown link, e.g. # [Gardener Extension for Alicloud provider](https://gardener.cloud):