Add 'borrowing' and 'consuming' to list of keywords (#303)

This list got missed in PR #173 when adding them to the reference.

Fixes: swiftlang/swift-book#300

Author: amartini51

TSPL.docc/ReferenceManual/LexicalStructure.md

@@ -247,7 +247,9 @@ so they must be escaped with backticks in that context.
 
 - Keywords used in declarations:
   `associatedtype`,
+  `borrowing`,
   `class`,
+  `consuming`,
   `deinit`,
   `enum`,
   `extension`,