Merge rust-bitcoin#5024: docs(CONTRIBUTING.md): Fix broken anchors

f53af9f docs(CONTRIBUTING.md): Fix broken anchors (BonyHanter83)

Pull request description:

  This updates CONTRIBUTING.md to fix two dead anchors that currently 404. The Table of Contents linked “CI and Merging” to #merging, but the markdown-generated anchor is #ci-and-merging; the ToC also referenced a “Policy” section that didn’t exist. I corrected the ToC link and added a short “Policy” section pointing to docs/policy.md.


ACKs for top commit:
  apoelstra:
    ACK f53af9f; successfully ran local tests; this is great, thanks!


Tree-SHA512: 6836ddda3ebeda37c03363d04c590a4935a0a378ba2352c3d45b4c9d55e9892ac5994293d143f06b6ad9940a4e7670125d369af22283e19cd769d8b4a140b3fa

Author: apoelstra

CONTRIBUTING.md

@@ -16,7 +16,7 @@ changes to this document in a pull request.
 - [Contribution workflow](#contribution-workflow)
   * [Preparing PRs](#preparing-prs)
   * [Peer review](#peer-review)
-  * [CI and Merging](#merging)
+  * [CI and Merging](#ci-and-merging)
   * [Repository maintainers](#repository-maintainers)
 - [Coding conventions](#coding-conventions)
   * [Naming conventions](#naming-conventions)
@@ -218,6 +218,10 @@ Use of `unsafe` code is prohibited unless there is a unanimous decision among
 library maintainers on the exclusion from this rule. In such cases there is a
 requirement to test unsafe code with sanitizers including Miri.
 
+### Policy
+
+For broader project policy and guidelines, see [policy.md](./docs/policy.md).
+
 ### API changes
 
 All PRs that change the public API of `rust-bitcoin` will be checked on CI for