Keep only the latest Rails release install stanza in README

Collapse the four near-identical per-version INSTALLATION blocks
(7.1 / 7.2 / 8.0 / 8.1) into a single Rails 8.1 block. Readers on
older supported Rails versions are pointed at the matching release
branch or Git tag for that version's README.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

README.md

@@ -6,49 +6,19 @@ Oracle enhanced adapter for ActiveRecord
 DESCRIPTION
 -----------
 
-Oracle enhanced ActiveRecord adapter provides Oracle database access from Ruby on Rails applications. Oracle enhanced adapter supports Ruby on Rails 7.1 through 8.1 and works with Oracle Database 10g and higher.
+Oracle enhanced ActiveRecord adapter provides Oracle database access from Ruby on Rails applications. This branch supports Ruby on Rails 8.1 and works with Oracle Database 10g and higher. For earlier Rails versions, see the corresponding release branch or Git tag.
 
 INSTALLATION
 ------------
-### Rails 8.1
 
-Oracle enhanced adapter version 8.1 supports Rails 8.1
-When using Ruby on Rails version 8.1 then in Gemfile include
+Oracle enhanced adapter version 8.1 supports Rails 8.1. In `Gemfile`:
 
 ```ruby
 # Use oracle as the database for Active Record
 gem 'activerecord-oracle_enhanced-adapter', '~> 8.1.0'
 ```
 
-### Rails 8.0
-
-Oracle enhanced adapter version 8.0 supports Rails 8.0
-When using Ruby on Rails version 8.0 then in Gemfile include
-
-```ruby
-# Use oracle as the database for Active Record
-gem 'activerecord-oracle_enhanced-adapter', '~> 8.0.0'
-```
-
-### Rails 7.2
-
-Oracle enhanced adapter version 7.2 supports Rails 7.2
-When using Ruby on Rails version 7.2 then in Gemfile include
-
-```ruby
-# Use oracle as the database for Active Record
-gem 'activerecord-oracle_enhanced-adapter', '~> 7.2.0'
-```
-
-### Rails 7.1
-
-Oracle enhanced adapter version 7.1 supports Rails 7.1
-When using Ruby on Rails version 7.1 then in Gemfile include
-
-```ruby
-# Use oracle as the database for Active Record
-gem 'activerecord-oracle_enhanced-adapter', '~> 7.1.0'
-```
+For earlier Rails versions, see the corresponding release branch or Git tag.
 
 USAGE
 -----