doc/go1: mention that the compiler catches TotalSize and NewReaderSize

Today is Size day and the compiler will reject old code using these functions.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5644053

doc/go1.html

@@ -875,8 +875,7 @@ If the argument size is too small or invalid, it is adjusted.
 
 <p>
 <em>Updating</em>:
-These functions are rarely used, and code must be updated by hand.
-All that is required is to drop the second return value.
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="crypto_elliptic">The crypto/elliptic package</h3>
@@ -937,7 +936,7 @@ In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
 
 <p>
 <em>Updating</em>:
-Code that depends on the function will need to be updated.
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="encoding_xml">The encoding/xml package</h3>

doc/go1.tmpl

@@ -779,8 +779,7 @@ If the argument size is too small or invalid, it is adjusted.
 
 <p>
 <em>Updating</em>:
-These functions are rarely used, and code must be updated by hand.
-All that is required is to drop the second return value.
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="crypto_elliptic">The crypto/elliptic package</h3>
@@ -841,7 +840,7 @@ In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
 
 <p>
 <em>Updating</em>:
-Code that depends on the function will need to be updated.
+What little code is affected will be caught by the compiler and must be updated by hand.
 </p>
 
 <h3 id="encoding_xml">The encoding/xml package</h3>