Document stringio cleanup guidance

Explain how to remove ambiguous stringio versions in docs.

Author: evolve75

CHANGELOG.md

@@ -13,6 +13,8 @@ Changes section to scan for breaking or behavioral changes.
 * Expand examples with traversal, update/delete, and JSON round-trip steps
   while aligning example data with the diagrammed structures.
 * Link to the full examples directory from the README.
+* Note that ambiguous `stringio` spec warnings can be resolved by removing
+  extra versions (for example, `gem cleanup stringio`).
 
 ### 3.0.0pre / 2026-02-08
 

CONTRIBUTING.md

@@ -24,6 +24,10 @@ Development dependencies (not required for installing the gem):
 * [mdl][] for markdown linting
 * [RuboCop][] for linting the code
 
+If RubyGems warns about ambiguous `stringio` specs in your dev gemset,
+remove the extra versions in this repo’s gemset (for example):
+`gem cleanup stringio`.
+
 ## Getting the Source
 
 You can download the latest released source code as a tar or zip file, as

Gemfile.lock

@@ -99,7 +99,7 @@ GEM
     simplecov-html (0.13.2)
     simplecov-lcov (0.9.0)
     simplecov_json_formatter (0.1.4)
-    stringio (3.2.0)
+    stringio (3.0.1)
     test-unit (3.7.7)
       power_assert
     tomlrb (2.0.4)