[skip vbump] closes #10 add badges and CRAN installation instructions

[rossfarrugia]

Thank you for your Pull Request! We have developed this task checklist from the Development Process Guide to help with the final steps of the process. Completing the below tasks helps to ensure our reviewers can maximize their time on your code as well as making sure the admiral codebase remains robust and consistent.

Please check off each taskbox as an acknowledgment that you completed the task or check off that it is not relevant to your Pull Request. This checklist is part of the Github Action workflows and the Pull Request will not be merged into the main branch until you have checked off each task.

• Place Closes #<insert_issue_number> into the beginning of your Pull Request Title (Use Edit button in top-right if you need to update)
• Code is formatted according to the tidyverse style guide. Run styler::style_file() to style R and Rmd files
• Updated relevant unit tests or have written new unit tests, which should consider realistic data scenarios and edge cases, e.g. empty datasets, errors, boundary cases etc. - See Unit Test Guide
• If you removed/replaced any function and/or function parameters, did you fully follow the deprecation guidance?
• Update to all relevant roxygen headers and examples, including keywords and families. Refer to the categorization of functions to tag appropriate keyword/family.
• Run devtools::document() so all .Rd files in the man folder and the NAMESPACE file in the project root are updated appropriately
• Address any updates needed for vignettes and/or templates
• Update NEWS.md under the header # admiralpeds (development version) if the changes pertain to a user-facing function (i.e. it has an @export tag) or documentation aimed at users (rather than developers)
• Build admiralpeds site pkgdown::build_site() and check that all affected examples are displayed correctly and that all new functions occur on the Reference page.
• Address or fix all lintr warnings and errors - lintr::lint_package()
• Run R CMD check locally and address all errors and warnings - devtools::check()
• Link the issue in the Development Section on the right hand side.
• Address all merge conflicts and resolve appropriately
• Pat yourself on the back for a job well done! Much love to your accomplishment!

[github-actions]

Package	Line Rate	Health
admiralpeds	99%	✔
Summary	99% (267 / 271)	✔

[Fanny-Gautier]

All badges appear well. CRAN installation update ok.