Update Mayring reference and add DOI

Added DOI for the Mayring reference and updated its details.

Author: tmaier-kettering

paper.bib

@@ -5,6 +5,7 @@ @book{saldana2021
   edition   = {4th},
   publisher = {SAGE Publications},
   address   = {London}
+  doi       = {10.4135/9781036235611}
 }
 
 @article{cohen1960,
@@ -18,14 +19,15 @@ @article{cohen1960
   doi     = {10.1177/001316446002000104}
 }
 
-@article{mayring2000,
+@article{mayring2022,
   author  = {Mayring, Philipp},
-  title   = {Qualitative Content Analysis},
-  journal = {Forum: Qualitative Social Research},
-  year    = {2000},
+  title   = {Qualitative Content Analysis: A Step-by-Step Guide},
+  journal = {Sage},
+  year    = {2022},
   volume  = {1},
   number  = {2},
-  url     = {https://www.qualitative-research.net/index.php/fqs/article/view/1089}
+  url     = {https://sk.sagepub.com/book/mono/qualitative-content-analysis-a-step-by-step-guide/toc}
+  doi     = {10.4135/9781036231798}
 }
 
 @techreport{openai2024,