Update summary for MethodImplOptions.AggressiveOptimization (#8024)

Author: AndyAyersMS

xml/System.Runtime.CompilerServices/MethodImplOptions.xml

@@ -143,7 +143,9 @@
       </ReturnValue>
       <MemberValue>512</MemberValue>
       <Docs>
-        <summary>The method contains a hot path and should be optimized.</summary>
+        <summary><para>The method contains code that should always be optimized by the just-in-time (JIT) compiler.</para>
+        <para>Use this attribute if running an unoptimized version of the method has undesirable effects, for instance causing too much overhead or extra memory allocation.</para>
+        <para>Methods with this attribute may not have optimal code generation. They bypass the first tier of <a href="/dotnet/core/runtime-config/compilation#tiered-compilation">Tiered Compilation</a> and therefore can't benefit from optimizations that rely on tiering, for example, <a href="/dotnet/core/runtime-config/compilation#profile-guided-optimization">Dynamic PGO</a> or optimizations based on initialized classes.</para></summary>
       </Docs>
     </Member>
     <Member MemberName="ForwardRef">