Merge pull request swiftlang#15143 from Vercantez/patch-2

Author: swift-ci

docs/OptimizationTips.rst

@@ -21,7 +21,7 @@ Enabling Optimizations
 ======================
 
 The first thing one should always do is to enable optimization. Swift provides
-three different optimization levels:
+four different optimization levels:
 
 - ``-Onone``: This is meant for normal development. It performs minimal
   optimizations and preserves all debug info.
@@ -35,6 +35,8 @@ three different optimization levels:
   result in undetected memory safety issues and integer overflows. Only use this
   if you have carefully reviewed that your code is safe with respect to integer
   overflow and type casts.
+- ``-Osize``: This is a special optimization mode where the compiler prioritizes
+  code size over performance.
 
 In the Xcode UI, one can modify the current optimization level as follows: