hooks/README: Fix some Markdown typos (e.g. missing runc target)

[wking]

I'd accidentally introduced these typos in #772.

[rhatdan]

bot, retest this please

[wking]

I'm not sure how Markdown fixes are leading to:

Error determining manifest MIME type for docker://busybox:latest
...
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x1f0 pc=0xa0fb0c]

goroutine 128 [running]:
testing.tRunner.func1(0xc4205002d0)
	/usr/lib/golang/src/testing/testing.go:742 +0x29d
panic(0xad1180, 0x116f030)
	/usr/lib/golang/src/runtime/panic.go:502 +0x229
github.com/projectatomic/libpod/libpod/image.(*Image).ID(...)
	/go/src/github.com/projectatomic/libpod/libpod/image/image.go:257
github.com/projectatomic/libpod/libpod/image.TestImage_New(0xc4205002d0)
	/go/src/github.com/projectatomic/libpod/libpod/image/image_test.go:132 +0x38c
testing.tRunner(0xc4205002d0, 0xbd0358)
	/usr/lib/golang/src/testing/testing.go:777 +0xd0
created by testing.(*T).Run
	/usr/lib/golang/src/testing/testing.go:824 +0x2e0
FAIL	github.com/projectatomic/libpod/libpod/image	25.636s

That seems like a pretty major flake.

[rhatdan]

@baude PTAL, It looks like there is a way to get an Image struct without a valid image field. If this is ok to happen then those return calls should be checking if i.image has been set and if not return "".

[TomSweeneyRedHat]

Changes LGTM, can't imagine they're causing test hiccups.

[mheon]

Probably a network flake in the image library unit tests. Those tests are not particularly durable, and will segfault fairly consistently if they fail to pull an image down. Should probably look into adding fault tolerance to them at some point.

[mheon]

bot, retest this please

[mheon]

LGTM once tests are green.

[mheon]

@rh-atomic-bot r+

[rh-atomic-bot]

📌 Commit a8e544c has been approved by mheon

[rh-atomic-bot]

⌛ Testing commit a8e544c with merge 31e3a50...

[rh-atomic-bot]

☀️ Test successful - status-papr
Approved by: mheon
Pushing 31e3a50 to master...