Auto merge of #5562 - flip1995:clippyup_up, r=phansch
Auto merge of #5562 - flip1995:clippyup_up, r=phansch

Update contributing section about syncing Clippy

[Rendered](https://github.com/flip1995/rust-clippy/blob/clippyup_up/CONTRIBUTING.md#fixing-build-failures-caused-by-rust)

r? @oli-obk Did I get the sync process right?

changelog: none

aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust