…javiereguiluz, wiese)

This PR was merged into the master branch.

Discussion
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Symfony Messenger component documentation

This pull-request adds some documentation for the Messenger component. As it is, it's extracted from the README built incrementally in the code pull-request.

I'm sure there will be lots to change when the implementation is merged :)

Commits
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c5306b8 Minor wording change
32403ea Update the documentation to reflect the latest changes
3fb973c Update based on comments
509e149 Add a documentation about middlewares and update based on reviews
fb88abc Add Messenger in the topics
a15752b Fix unresolved reference
25c0b6e It helps multiple applications  Please enter the commit message for your changes. Lines starting
bcfae23 Finish the documentation about the custom adapter
2493c90 Update typos and missing reference
31a56ee Uses `::` to display as code blocks
5c828e4 Update the documentation a bit, and add more FrameworkBundle documentation
88ba8fe Merge pull request #1 from wiese/patch-3
b26de80 minor doc fixes for the Message component
b40bc71 Fixed the RST syntax issues
585491d Move the documentation from the main PR to RST format.