[clangd] Mention indexing in docs.
Reviewers: sammccall
Subscribers: ilya-biryukov, ioeric, MaskRay, jkorous, arphaman, cfe-commits
Differential Revision: https://reviews.llvm.org/D57392
git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@353423 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/clangd.rst b/docs/clangd.rst
index 84696e3..0843bca 100644
--- a/docs/clangd.rst
+++ b/docs/clangd.rst
@@ -143,6 +143,25 @@
:program:`Emacs` provides `lsp-mode <github.com/emacs-lsp/lsp-mode>`_ and
`Eglot <https://github.com/joaotavora/eglot>`_ plugins for LSP integration.
+Project-wide Index
+==================
+
+By default :program:`Clangd` only has a view on symbols coming from files you
+are currently editing. You can extend this view to whole project by providing a
+project-wide index to :program:`Clangd`.
+
+There are two ways you can generate a project-wide index for clangd:
+
+- Passing experimental `-background-index` commandline argument, which will
+ incrementally build an index of projects that you work on and make use of that
+ in clangd automatically.
+- Generate an index file using `clangd-indexer
+ <https://github.com/llvm-mirror/clang-tools-extra/blob/master/clangd/indexer/IndexerMain.cpp>`_
+ Afterwards you can pass generated index file to clangd using
+ `-index-file=/path/to/index_file`. *Note that clangd-indexer isn't included
+ alongside clangd in the standard clang-tools package. You will likely have to
+ build from source to use this option*
+
Getting Involved
==================
