feat docs: minor tweaks for LRU docs

Tests: на прод не влияет
commit_hash:6be176ee1f1c9c16793fbebf287975b660037e90

Author: apolukhin

scripts/docs/en/userver/libraries/multi_index_lru.md

@@ -1,4 +1,4 @@
-# LRU Container
+# MultiIndex LRU Container
 
 ## Introduction
 

scripts/docs/en/userver/lru_cache.md

@@ -48,6 +48,8 @@ Here's a brief introduction into LRU types:
 * Concurrency-safe expirable container @ref cache::ExpirableLruCache with precise
   control over the expiration logic.
 * Concurrency-safe non-expirable container @ref cache::NWayLRU.
+* Non-expirable @ref scripts/docs/en/userver/libraries/multi_index_lru.md that provides the same
+  concurrency guarantees as the standard library containers. Based on Boost.MultiIndex C++ library.
 * Non-expirable container @ref cache::LruMap that provides the same concurrency
   guarantees as the standard library containers.
 * Non-expirable @ref cache::LruSet that provides the same concurrency guarantees as

scripts/docs/en/userver/roadmap_and_changelog.md

@@ -41,7 +41,8 @@ Changelog news also go to the
   structured details following Google's error model
 * Added a @ref utils::statistics::RegisterWriterScope for safe and easy registration of statistics.
 * No more need to call `CacheUpdateTrait::StartPeriodicUpdates()` from your caching components.  
-* Implemented a Multi Index LRU container, thanks to [hzhdlrp](https://github.com/hzhdlrp).
+* Implemented a @ref scripts/docs/en/userver/libraries/multi_index_lru.md, thanks to
+  [hzhdlrp](https://github.com/hzhdlrp).
 * Statement name is now logged when using @ref storages::postgres::Portal.
 * Monitor port is now opened before all the components and handlers are started, leading to more control and
   information on service start.