Adds CHANGELOG entry for #89

Author: weierophinney

CHANGELOG.md

@@ -8,7 +8,11 @@ Releases prior to 1.2.0 did not have entries.
 
 ### Added
 
-- Nothing.
+- [#89](https://github.com/zendframework/zenddiagnostics/pull/89) adds full documentation at https://docs.zendframework.com/zend-diagnostics
+
+- [#89](https://github.com/zendframework/zenddiagnostics/pull/89) adds support for Guzzle 6. While support was previously
+  added, it included syntax that emitted deprecation notices; it now
+  correctly uses the Guzzle HTTP client.
 
 ### Changed
 
@@ -20,7 +24,11 @@ Releases prior to 1.2.0 did not have entries.
 
 ### Removed
 
-- Nothing.
+- [#89](https://github.com/zendframework/zenddiagnostics/pull/89) removes support for Guzzle versions 3 and 4 when using the
+  Guzzle HTTP checks. Guzzle 3 has been EOL for approximately 5 years, while version
+  4 is incompatible with PHP versions 7.1 and 7.2 due to a syntax issue that only
+  those versions detect correctly. Since version 5 has been available for almost 4
+  years, users who are on older versions should upgrade.
 
 ### Fixed