crfs: fix a typo and misleading detail about TAR files
crfs: fix a typo and misleading detail about TAR files

Change-Id: I8e01a5087a61694d932dcf594351845d80473258
Reviewed-on: https://go-review.googlesource.com/c/build/+/167758
Reviewed-by: Maisem Ali <7c693fc9861ca64bf2c3972e928f93902ea46711@google.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build