Add important information about citing id, info to define a book-entry and newspaper-entry

README.md

@@ -325,8 +325,12 @@ For mor information you can visit https://www.bibtex.com/e/entry-types/. There a
 To define web sources, I've found the type "misc" perfect. You can always use the following template and fill in the
 variables in with blanks.
 
+> It's **very important** to fill out the variable `<CITING_ID>`. This variable is used to reference the reference in
+> the
+> text to the correct BibTeX entry.
+
 ```latex
-@misc{CitingId,
+@misc{<CITING_ID>,
 author = {<AUTHOR_NAME>},
 title = {<WEBSITE_TITLE>},
 date = {<PUBLISHED_DATE>},
@@ -336,3 +340,34 @@ note = {Abgerufen am <VIEWED_ON_DATE>},
 howpublished = {<URL_TO_PAGE>}
 }
 ```
+
+### Defining a Book-Source
+
+To define a book source, it's basically the same principle as a web source. You just got other variables / fields to
+fill in.
+
+```latex
+@book{<CITING_ID>,
+author    = {<AUTHOR_NAME>},
+title     = {<BOOK_TITLE>},
+publisher = {<PUBLISHER>},
+year      = {<YEAR_PUBLISHED>},
+pages = {<PAGES_RELEVANT>}
+}
+```
+
+### Defining a Newspaper-Source
+
+Newspaper sources work the same. You got a few more variables to fill, because there are more informations relevant.
+
+```latex
+@article{<CITING_ID>,
+  author   = {<AUTHOR_NAME>},
+  title    = {<ARTICLE_TITLE>},
+  journal  = {<NEWSPAPER_NAME>},
+  year     = {<YEAR_PUBLISHED>},
+  volume   = {<NEWSPAPER_VOLUME>},
+  number   = {<NUMBER>},
+  pages    = {<PAGES_OF_NEWSPAPER_RELEVANT>},
+}
+```