Document the non-guava String.split fix

Fixes #899

RELNOTES: N/A

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=182158360

docs/bugpattern/StringSplit.md

@@ -13,3 +13,9 @@ Prefer guava's
 [`String.splitter`](http://google.github.io/guava/releases/23.0/api/docs/com/google/common/base/Splitter.html),
 which has more predicitable behaviour and provides explicit control over the
 handling of empty strings and the trimming of whitespace.
+
+Alternately, consider using [`String.split(String,
+int)`](https://docs.oracle.com/javase/9/docs/api/java/lang/String.html#split-java.lang.String-int-)
+and setting an explicit 'limit'.
+
+TIP: consider extracting the `Splitter` instance to a static final field.

docs/bugpattern/StringSplitter.md

@@ -14,4 +14,8 @@ Prefer guava's
 which has more predicitable behaviour and provides explicit control over the
 handling of empty strings and the trimming of whitespace.
 
+Alternately, consider using [`String.split(String,
+int)`](https://docs.oracle.com/javase/9/docs/api/java/lang/String.html#split-java.lang.String-int-)
+and setting an explicit 'limit'.
+
 TIP: consider extracting the `Splitter` instance to a static final field.