add search var to sample env

Adding MAX_SEARCH RESULTS to the env sample file, and documented

.env.production.sample

@@ -175,6 +175,10 @@ STREAMING_CLUSTER_NUM=1
 # Maximum length of audio uploads in seconds
 # MAX_AUDIO_LENGTH=60
 
+# Maximum number of search results
+# Only really matters if elasticsearch is enabled
+# MAX_SEARCH_RESULTS=100
+
 # LDAP authentication (optional)
 # LDAP_ENABLED=true
 # LDAP_HOST=localhost