Merge branch 'm-iv-type-score' of github.com:DoubleML/doubleml-docs into m-release-notes-0.5.0

Author: MalteKurz

doc/conf.py

@@ -129,6 +129,7 @@
     'https://doi.org/10.1093/ectj/utaa001',  # Valid DOI; Causes 403 Client Error: Forbidden for url:...
     'https://doi.org/10.1111/ectj.12097',  # Valid DOI; Causes 403 Client Error: Forbidden for url:...
     'https://doi.org/10.2307/2171802',  # Valid DOI; Causes 403 Client Error: Forbidden for url:...
+    'https://doi.org/10.2307/1912705',  # Valid DOI; Causes 403 Client Error: Forbidden for url:...
 ]
 
 # To execute R code via jupyter-execute one needs to install the R kernel for jupyter