AIP-193: Address review comments

Author: jskeet

aip/general/0193.md

@@ -100,7 +100,7 @@ The reason **must** be at most 63 characters and match a regular expression of
 `[A-Z][A-Z0-9_]+[A-Z0-9]`. (This is UPPER_SNAKE_CASE, without leading
 or trailing underscores, and without leading digits.)
 
-The reason should be terse, but meaningful enough for a human reader to
+The reason **should** be terse, but meaningful enough for a human reader to
 understand what the reason refers to.
 
 Good examples:
@@ -234,7 +234,7 @@ authentication.
 ### Error messages
 
 Textual error messages can be present in both `Status.message` and
-`LocalizedMessage.message` fields. Messages should be succinct but
+`LocalizedMessage.message` fields. Messages **should** be succinct but
 actionable, with request-specific information (such as a resource name
 or region) providing precise details where appropriate. Any request-specific
 details **must** be present in [`ErrorInfo.metadata`](#errorinfo).