Add a link to Mojo documentation main page to the document index

Change-Id: I7c6d15d75fd6ea4a936729bc2b07445778fae165
Reviewed-on: https://chromium-review.googlesource.com/c/1281867
Reviewed-by: Ken Rockot <[email protected]>
Commit-Queue: Oksana Zhuravlova <[email protected]>
Cr-Commit-Position: refs/heads/master@{#600057}
diff --git a/docs/README.md b/docs/README.md
index 86db0ce7..579c5f4 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -330,6 +330,7 @@
     install Chromium OS on VMWare.
 *   [User Data Directory](user_data_dir.md) - How the user data and cache
     directories are determined on all platforms.
+*   [Mojo](../mojo/README.md) - IPC mechanism used by services.
 
 ### Probably Obsolete
 *   [TPM Quick Reference](tpm_quick_ref.md) - Trusted Platform Module notes.