docs: add a note about MissingPluginException after installing without a fresh restart

[karimkod]

Description

add a note about MissingPluginException after installing without a fresh restart.
This exception has been reported in the issues several times, and I think it's because most of the devs add the package and don't fully restart the app to embed the platform code needed see issues

Adding it to the documentation may save time for devs and prevent creating other related issues.

Related Issues

see issues

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[karimkod]

Added it only on share_plus, maybe we need to add them to all other packages where this error can occur.

Should I?

[miquelbeltran]

Hi, I get what you mean, and I appreciate the good intentions, but I think this that this is basic understand on how Flutter works.

Compilation issues are mostly reported by people that don't invest time researching how to fix them, and I don't believe they even read the READMEs or look for existing tickets. Our issue templates already has instructions in them on how to fix the most basic compilation and running issues, but they still blindly create the tickets.

Learned helplessness is definitely a wide problem in today's dev community.