Built from:
92c83ad8a4fd6224cf6319a60b399854f55b38ebe9d297c942408b792b1a9efa  cmake-3.5.0.tar.gz

Update instructions in the UPDATING file.

Change-Id: I49d3f5ef353347c446a04797719227e9793e3e0d
Reviewed-on: https://boringssl-review.googlesource.com/7414
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

Built from:
45f4d3fa8a2f61cc092ae461aac4cac1bab4ac6706f98274ea7f314dd315c6d0  cmake-3.1.3.tar.gz

We're still waiting on infra before the buildbot master is up, but let's get
this ready for when we do; it should be fairly easy.

BUG=430237

Change-Id: I3a414743d44052e1aa48759fa5f125db4d4913b5
Reviewed-on: https://boringssl-review.googlesource.com/3670
Reviewed-by: Adam Langley <agl@google.com>