-[Docs] copyedit docs title

Summary: Updated web/docs/src/pages/index.js to reflect change requested in task T1966.

Test Plan: navigate to web/docs/src/pages/index.js, ensure updated copy is correct.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10488