[7.x] [DOCS] Update docs for 'synced flush' and 'SLM' APIs (#972) (#976)

api/api/indices.flush_synced.js

@@ -38,6 +38,11 @@ function buildIndicesFlushSynced (opts) {
     filterPath: 'filter_path'
   }
 
+  /**
+   * Perform a indices.flush_synced request
+   * Performs a synced flush operation on one or more indices.
+   * https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-synced-flush-api.html
+   */
   return function indicesFlushSynced (params, options, callback) {
     options = options || {}
     if (typeof options === 'function') {

docs/reference.asciidoc

@@ -2497,7 +2497,7 @@ client.indices.flushSynced({
   expand_wildcards: 'open' | 'closed' | 'none' | 'all'
 })
 ----
-link:{ref}/indices-flush.html#synced-flush-api[Reference]
+link:{ref}/indices-synced-flush-api.html[Reference]
 [cols=2*]
 |===
 |`index`