RFR: Clearly state that users should create branch [v2]

[Jesper Wilhelmsson]

On Tue, 17 Jan 2023 21:59:00 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> A recent PR submission to the JDK made me aware that the guide does not strongly enough emphasize the importance of creating a separate branch. 
>> 
>> (If you do put your changes directly in `master`, the Skara bots will put up harsh warnings, which is not a nice way to welcome someone who has tried to do everything right, including reading the guide)
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo
>   
>   Co-authored-by: Alexey Ivanov <alexey.ivanov at oracle.com>

"should" is still just a recommendation. If you want to make this authoritative "must" is a better choice.

"messy and complicated" is very subjective. Could it be described more clearly what will actually be the problem?

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Changes requested by jwilhelm (Lead).

PR: https://git.openjdk.org/guide/pull/94