Content: Create introduction to AnitaB.org Open Source section for home page

### Is your feature request related to a problem? Please describe.
As a user,
I need a brief yet engaging introduction about AnitaB.org Open Source.

### Mocks

### Acceptance Criteria

**Update [Required]**

- [ ] The description should be engaging and should encourage the user to check the other sections of website and participate in the community.

**Definition of Done**

- [ ] All of the required items are completed.
- [ ] Approval by 1 mentor.

**Estimation**
1-2 days

Start at the website home page and compare its current Open Source section with the linked mock. Draft a brief, engaging introduction that directs users toward the other website sections and community participation; the work is done when the description meets the acceptance criterion and receives mentor approval.

Written by the indexing model from the issue text.