Rollup merge of #74296 - Lynoure:rfind-doc-improvement, r=hanna-kruppe
Rollup merge of #74296 - Lynoure:rfind-doc-improvement, r=hanna-kruppe

Clarify the description for rfind

Changes the wording in rfind description to be clearer and the example code to illustrate the difference between
find and rfind

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