Ignore cr-???-??? directories in top-level

Code Review sub-directories should be ignored in the top-level directory
but allowed in the src directory.  This is directly analogous to the
so-????-???? directories.

.gitignore

@@ -38,6 +38,7 @@ Untracked/
 [a-z][a-z][a-z][a-z][0-9][0-9]
 awk.script
 core
+cr-[0-9][0-9][0-9]-[0-9][0-9][0-9]
 cscope.out
 data
 data.[0-9]
@@ -62,4 +63,5 @@ tmp/
 !inc
 !lib
 !src
+!src/cr-[0-9][0-9][0-9]-[0-9][0-9][0-9]
 !src/so-[0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]/