Update fo docs

add flag section
ImGuiFileDialogFlags_DontShowHiddenFiles => added from issue #51

Author: aiekick

ImGuiFileDialog.h

@@ -288,7 +288,6 @@ Example code :
 Load => ImGuiFileDialog::Instance()->DeserializeBookmarks(bookmarString);
 Save => std::string bookmarkString = ImGuiFileDialog::Instance()->SerializeBookmarks();
 
-
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 ## Path Edition :
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@@ -343,6 +342,14 @@ Example code :
 #define OverWriteDialogConfirmButtonString "Confirm"
 #define OverWriteDialogCancelButtonString "Cancel"
 
+-----------------------------------------------------------------------------------------------------------------
+## Flags :
+-----------------------------------------------------------------------------------------------------------------
+
+flag must be specified in OpenDialog or OpenModal
+* ImGuiFileDialogFlags_ConfirmOverwrite 	=> show confirm to overwrite dialog
+* ImGuiFileDialogFlags_DontShowHiddenFiles 	=> dont show hidden file (file starting with a .)
+
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 ## Open / Save dialog Behavior :
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