metainfo: Fix appstreamcli validate warnings

[ryonakano]

This fixes some warnings from appstreamcli validate command which I noticed while reviewing your app. This is just a warning and not a critical error, so you don't need to publish another release soon after merging this.

Before

[ryo@b760m ~/work/tmp/Jorts (main $=)]$ appstreamcli validate data/jorts.metainfo.xml.in
I: io.github.ellie_commons.jorts:10: description-first-para-too-short
     Colourful little sticky notes for all of your thoughts :)
W: io.github.ellie_commons.jorts:29: url-not-reachable
     https://github.com/ellie_commons/jorts - URL was not found on the server.
W: io.github.ellie_commons.jorts:30: url-not-reachable
     https://github.com/ellie_commons/jorts/issues - URL was not found on the server.
W: io.github.ellie_commons.jorts:31: url-not-reachable
     https://github.com/ellie_commons/jorts/issues - URL was not found on the server.
W: io.github.ellie_commons.jorts:32: url-not-reachable
     https://github.com/ellie_commons/jorts/blob/main/po/README.md - URL was not found on the
     server.
W: io.github.ellie_commons.jorts:67: tag-empty translation

✘ Validation failed: warnings: 5, infos: 1
[ryo@b760m ~/work/tmp/Jorts (main $=)]$

After

[ryo@b760m ~/work/tmp/Jorts (ryonakano/fix-metainfo-warnings)]$ appstreamcli validate data/jorts.metainfo.xml.in
I: io.github.ellie_commons.jorts:10: description-first-para-too-short
     Colourful little sticky notes for all of your thoughts :)

✔ Validation was successful: infos: 1
[ryo@b760m ~/work/tmp/Jorts (ryonakano/fix-metainfo-warnings)]$

[teamcons]

Thank you