docs: Add missing symbol in README.md (#21640)

Author: liangmulu

docs/architecture/README.md

@@ -36,7 +36,7 @@ Read about the [PROCESS](./PROCESS.md).
 
 ### Use RFC 2119 Keywords
 
-When writing ADRs, follow the same best practices for writing RFCs. When writing RFCs, key words are used to signify the requirements in the specification. These words are often capitalized: "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL. They are to be interpreted as described in [RFC 2119](https://datatracker.ietf.org/doc/html/rfc2119).
+When writing ADRs, follow the same best practices for writing RFCs. When writing RFCs, key words are used to signify the requirements in the specification. These words are often capitalized: "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL". They are to be interpreted as described in [RFC 2119](https://datatracker.ietf.org/doc/html/rfc2119).
 
 ## ADR Table of Contents