bip3: rename 'shareholder' to 'stakeholder'

Shareholder refers to an individual or a legal entity owning a share of a company's share capital.
Since the Bitcoin system is not a company, but different actors across the industry have a stake in
its operation, i think the word "stakeholder" better conveys the intended meaning of the original
author here.

Author: darosior

bip-0003.md

@@ -75,7 +75,7 @@ allows any community member to retain a complete copy of the archive easily.
 The BIPs repository is not a tool to track acceptance[^acceptance], adoption, or community consensus on BIPs, beyond
 providing a brief overview of BIP statuses (see [Workflow](#workflow) below) to the audience.
 There is no formal or informal decision body that governs Bitcoin development or decides acceptance of BIPs. Bitcoin
-development emerges from the participation of shareholders across the ecosystem.
+development emerges from the participation of stakeholders across the ecosystem.
 
 ## BIP Format and Structure