Fix: Navigation titles for SDKs was "Index"

[hoh]

This is less clear "Introduction".

Solution: Rename the titles for the SDKs to "Introduction"

[github-actions[bot]]

Deployed (not pinned) on:

• https://ipfs-2.aleph.im/ipfs/QmdQHX9ghCzuhism8sLEXYcCC3KqpZzxBVw9gGYFmJNqWA
• https://beta.docs.aleph.im/ (may be overriden anytime by another PR)