chore: release prep — MIT badge, citation section, CITATION v0.4.0

- README: add MIT license badge, add ## Citation section
- inst/CITATION: bump version 0.2.0 → 0.4.0, add email/ORCID to author,
  add header field

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: bbuchsbaum

README.md

@@ -13,6 +13,7 @@ coverage](https://codecov.io/gh/bbuchsbaum/bidser/branch/master/graph/badge.svg)
 experimental](https://img.shields.io/badge/lifecycle-experimental-orange.svg)](https://lifecycle.r-lib.org/articles/stages.html#experimental)
 [![CRAN
 status](https://www.r-pkg.org/badges/version/bidser)](https://CRAN.R-project.org/package=bidser)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 <!-- badges: end -->
 
 [BIDS](https://bids.neuroimaging.io/) in R – (it’s a start!)
@@ -35,6 +36,12 @@ devtools::install_github("bbuchsbaum/bidser")
 
 See <https://bbuchsbaum.github.io/bidser/articles/quickstart.html>
 
+## Citation
+
+If you use bidser in published work, please cite:
+
+Buchsbaum, B. (2026). *bidser: Work with Brain Imaging Data Structure (BIDS) Projects*. R package version 0.4.0. <https://github.com/bbuchsbaum/bidser>
+
 <!-- albersdown:theme-note:start -->
 ## Albers theme
 This package uses the albersdown theme. Existing vignette theme hooks are replaced so `albers.css` and local `albers.js` render consistently on CRAN and GitHub Pages. The defaults are configured via `params$family` and `params$preset` (family = 'red', preset = 'homage'). The pkgdown site uses `template: { package: albersdown }` together with generated `pkgdown/extra.css` and `pkgdown/extra.js` so the theme is linked and activated on site pages.

inst/CITATION

@@ -1,10 +1,13 @@
 bibentry(
   bibtype  = "Manual",
   title    = "bidser: Work with Brain Imaging Data Structure (BIDS) Projects",
-  author   = person("Bradley", "Buchsbaum"),
+  author   = person("Bradley", "Buchsbaum", email = "brad.buchsbaum@gmail.com",
+                    role = c("aut", "cre"),
+                    comment = c(ORCID = "0000-0002-1108-4866")),
   year     = "2026",
-  note     = "R package version 0.2.0",
-  url      = "https://github.com/bbuchsbaum/bidser"
+  note     = "R package version 0.4.0",
+  url      = "https://github.com/bbuchsbaum/bidser",
+  header   = "To cite bidser in publications use:"
 )
 
 bibentry(