Tags file reading is now off by default

As the updated docs now say, this is off by default because it makes Vim slow if
your tags are on a network location.

README.md

@@ -748,9 +748,12 @@ format from "plain" ctags is NOT supported. Ctags needs to be called with the
 
 See the _FAQ_ for pointers if YCM does not appear to read your tag files.
 
-Default: `1`
+This option is off by default because it makes Vim slower if your tags are on a
+network directory.
+
+Default: `0`
 
-    let g:ycm_collect_identifiers_from_tags_files = 1
+    let g:ycm_collect_identifiers_from_tags_files = 0
 
 ### The `g:ycm_seed_identifiers_with_syntax` option
 
@@ -1147,6 +1150,8 @@ So just go through the installation guide and make sure you are using a correct
 
 ### YCM does not read identifiers from my tags files
 
+First, put `let g:ycm_collect_identifiers_from_tags_files = 1` in your vimrc.
+
 Make sure you are using [Exuberant Ctags][exuberant-ctags] to produce your tags
 files since the only supported tag format is the [Exuberant Ctags
 format][ctags-format]. The format from "plain" ctags is NOT supported. The

plugin/youcompleteme.vim

@@ -98,7 +98,7 @@ let g:ycm_collect_identifiers_from_comments_and_strings =
       \ get( g:, 'ycm_collect_identifiers_from_comments_and_strings', 0 )
 
 let g:ycm_collect_identifiers_from_tags_files =
-      \ get( g:, 'ycm_collect_identifiers_from_tags_files', 1 )
+      \ get( g:, 'ycm_collect_identifiers_from_tags_files', 0 )
 
 let g:ycm_seed_identifiers_with_syntax =
       \ get( g:, 'ycm_seed_identifiers_with_syntax', 0 )