Add clang/docs/SanitizerCoverage.rst

Moved from https://code.google.com/p/address-sanitizer/wiki/AsanCoverage

llvm-svn: 235643
diff --git a/clang/docs/index.rst b/clang/docs/index.rst
index 67bdf68..a3c8ffb 100644
--- a/clang/docs/index.rst
+++ b/clang/docs/index.rst
@@ -26,6 +26,7 @@
    MemorySanitizer
    DataFlowSanitizer
    LeakSanitizer
+   SanitizerCoverage
    SanitizerSpecialCaseList
    ControlFlowIntegrity
    Modules