[Docs] 'Limitations' should be a subsection

The 'Limitations' section in thedocumentation for
readability-misleading-indentation should be a subsection, as otherwise the link
to 'Limitations' isn't indented in the 'Clang-Tidy Checks' documentation page.

llvm-svn: 295471

clang-tools-extra/docs/clang-tidy/checks/readability-misleading-indentation.rst

@@ -32,7 +32,7 @@ Examples:
     foo2();  // Not guarded by if(cond1).
 
 Limitations
-===========
+-----------
 
 Note that this check only works as expected when the tabs or spaces are used
 consistently and not mixed.