issues.dbk: Add section for fcitx/fcitx5 mutual conflict

Package fcitx and fcitx5 now mutually conflict with each other. Document that users should determine which version of fcitx shall be kept during the OS upgrade.

cc @zhsj @mwei

merged

As nobody commented on it, I am merging this Merge Request. Please let me know if it needs further polishing.

Please don't do that again. We're busy, no need to rush it through.

@JustinBRye, I suspect you'll have a language nit-pick here or there.

Nothing critical, but I would like to avoid "package X and Y" (twice), and add an article for "^the^ upstream author"... or maybe just turn it into a vague "upstream":

      <title>Fcitx versions no longer co-installable</title>
      <para>
        The packages <systemitem role="package">fcitx</systemitem> and
        <systemitem role="package">fcitx5</systemitem> provide version 4 and
        version 5 of the popular Fcitx Input Method Framework. Following
        upstream's recommendation, they can no longer be co-installed

We might also drop the word "previous" in the mailinglist pointer ("the previous announcement posted in the mailing list").