[gnome-builder] doc: Document search symbol prefixes

[Christian Hergert <chergert src gnome org>]

commit 93d5b3959d83bd1aa09a6941c4e90ad582dead71
Author: albfan <albertofanjul gmail com>
Date:   Sun Oct 15 12:18:42 2017 +0200

    doc: Document search symbol prefixes
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789005

 doc/howto/search_for_symbol.rst |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)
---
diff --git a/doc/howto/search_for_symbol.rst b/doc/howto/search_for_symbol.rst
index 5d52b33..10a9030 100644
--- a/doc/howto/search_for_symbol.rst
+++ b/doc/howto/search_for_symbol.rst
@@ -9,6 +9,17 @@ Then start typing the name of the symbol.
 Fuzzy searching is supported.
 For example, searching for ``GcWin`` might match the symbol ``GcalWindow``.
 
+Filtering searches:
+You can narrow results prefixing searches with this keys:
+- ``f`` for functions
+- ``v`` for variables
+- ``s`` for structs
+- ``u`` for unions
+- ``e`` for enums
+- ``c`` for class
+- ``a`` for constants
+- ``m`` for macros
+
 Press ``Up`` or ``Down`` arrows to move between the results.
 Press ``Enter`` to activate the search result and jump to the symbol.
 You can press ``Escape`` to return to the editor.