Update writing-e2e-tests doc

[pratikjagrut]

Description of the change:
Adding one-liner information about --namespace flag.

Motivation for the change:
I was under the impression that operator-sdk test local ./test/e2e --up-local --namespace=memcached will create namespece=memcached and when I tried the command it was failing due to namespaces "memcached" not found and for this, I raised an issue #2014. But later I got to know that it won't create any namespace but we need to specify the namespace that it should watch for changes in. So I thought it's a good piece of information and should have a place in the doc.

[camilamacedo86]

I think is too long the sentence, also IMHO it would be better bellow the phase as a NOTE in the doc. WDYT could we change it?

[pratikjagrut]

Note: the --up-local flag requires the --namespace flag: NOTE: The command will NOT create the --namespace. Then, be sure that you are specifying a valid namespace.
Are you suggesting something like this?
Wouldn't it be the note followed by a note, which extends first note?

[camilamacedo86]

I am suggesting:

• Do not perform changes in the current explanation
• Then, just add a NOTE: in the next line and not in the same paragraph.

WDYT?

[pratikjagrut]

.....(Note: the --up-local flag requires the --namespace flag).

NOTE: The command will NOT create the namespace. Then, be sure that you are specifying a valid namespace.

Something like this!
This is doable, and yeah more elegant.

[camilamacedo86]

It is in the same line which is not the docs standards. The note in the same line with () makes harder the understanding.

See the following example.

operator-sdk/doc/user/unit-testing.md

Line 155 in 491cdf6

**NOTE**: A unit test checking more cases can be found in our [`samples repo`][code-test-example].

[pratikjagrut]

Ok, so I should remove the existing note from the paragraph and add a new note to the next line but not in the same paragraph.
paragraph...

**NOTE**: The --up-local flag requires the --namespace flag and the command will NOT create the --namespace. Then, be sure that you are specifying a valid namespace

Something like this! This was your code suggestion!

[pratikjagrut]

Committed changes have a look if its OK or not?

[camilamacedo86]

👍 great!
Tks for the contribution.

/lgtm
/approve

[camilamacedo86]

/test marker

[camilamacedo86]

/test e2e-aws-go

[camilamacedo86]

Very small nit NOTE in the docs. So, I am merging it.