docs: describe configuration for error-strings rule

Author: alexandear

RULES_DESCRIPTIONS.md

@@ -456,10 +456,19 @@ _Configuration_: N/A
 ## error-strings
 
 _Description_: By convention, for better readability, error messages should not be capitalized or end with punctuation or a newline.
+By default, the rule analyzes functions for creating errors from `fmt`, `errors`, and `github.com/pkg/errors`.
+Optionally, the rule can be configured to analyze user functions that create errors.
 
 More information [here](https://go.dev/wiki/CodeReviewComments#error-strings)
 
-_Configuration_: N/A
+_Configuration_: ([]string) the list of additional error functions to check. The format  of values is `package.FunctionName`.
+
+Example:
+
+```toml
+[rule.error-strings]
+  arguments = ["xerrors.Errorf"]
+```
 
 ## errorf