[analyzer] Add check::BeginFunction to CheckerDocumentation checks. NFC.

This was an oversight from when I added BeginFunction support in r261293.

llvm-svn: 276950
diff --git a/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp b/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
index 74d05e2..86764c9 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CheckerDocumentation.cpp
@@ -45,6 +45,7 @@
                                        check::Location,
                                        check::Bind,
                                        check::DeadSymbols,
+                                       check::BeginFunction,
                                        check::EndFunction,
                                        check::EndAnalysis,
                                        check::EndOfTranslationUnit,