Update README.md

the "*" match the last available release of the repo, which is for now the 1.1 branch, (= the 1.1.1 tag). Since various important issues were fixed in the dev-master (by example: only the dev-master in compatible with the stable release of Sonata Page), & if you do not plan to release a new branch in the next few days, I suggest to change the package version in the install documentation.
Merge pull request #26 from ronanguilloux/patch-1

Update README.md