Update repository README to include a link to releases page

[ptitzler]

Since version 3.5.x we've published a release summary on the Elyra releases page that highlights new features and includes a complete list of contributions. Unless the changelog, this page contains a description of new features and changes, making it easier for users to understand what's new and exciting.

What changes were proposed in this pull request?

• Add a link to the releases page to the overview section of the repository README.
• Replace the changelog link with the releases link in the binder section

How was this pull request tested?

👀

Developer's Certificate of Origin 1.1

   By making a contribution to this project, I certify that:

   (a) The contribution was created in whole or in part by me and I
       have the right to submit it under the Apache License 2.0; or

   (b) The contribution is based upon previous work that, to the best
       of my knowledge, is covered under an appropriate open source
       license and I have the right under that license to submit that
       work with modifications, whether created in whole or in part
       by me, under the same open source license (unless I am
       permitted to submit under a different license), as indicated
       in the file; or

   (c) The contribution was provided directly to me by some other
       person who certified (a), (b) or (c) and I have not modified
       it.

   (d) I understand and agree that this project and the contribution
       are public and that a record of the contribution (including all
       personal information I submit with it, including my sign-off) is
       maintained indefinitely and may be redistributed consistent with
       this project or the open source license(s) involved.

[elyra-bot]

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