doc: fixed release script to add version to the pdfs

And amended ReleaseNotes with exact version and tagging date

Docs/release.sh

@@ -294,6 +294,9 @@ rm -rf .git*
 
 # Create signatures and move files
 for f in *.pdf ; do
+    nopdf=${f//.pdf}
+    mv $f $nopdf-${_tag_no_v}.pdf
+    f=$nopdf-${_tag_no_v}.pdf
     sign $f
     store $f
     checksums $f

ReleaseNotes.md

@@ -6,7 +6,7 @@ grouped under headings representing past (and upcoming) releases.
 
 # 4.1.X versions
 
-## 4.1 (2021-   )   FUTURE Feature release
+## 4.1.5 (2021-01-27)  Feature release
 
 ### Backward compatibility issues