Improved comments for 'References' for clarity.

Feedback - Common mistakes from 2019.md

@@ -55,15 +55,15 @@
 
 # References
 
-- Not referencing the first paper that proved a fact, e.g. that TSP is NP-hard.
+- Not referencing the **first paper** that proved a fact.
 - Quoting data/fact without referencing. Where did it come from? Your own experiments or is it secondary data?
 - List of references not in alphabetical order by first author surname.
-- Some references are referenced as if they were a website when in fact they are published (No need to give URL for every entry, especially books).
+- Some references are cited as if they were a website when in fact they are published. (No need to give URL for every entry, especially books.)
 - Some references lack crucial information such as venue of publication.
-- Students relied on unreliable websites rather than formally published sources.
-- In-text citations look like "(Author, date)", not like e.g. [1], etc.
-- Not all references listed at the end were cited in text.
-- "et al." is used in in-text citations, but you must provide the full list of authors in the list of references (i.e. do not use "et al." here).
+- Students relied on unreliable websites, rather than formally published sources.
+- Not following the referencing style standard. Correct in-text citations should look like "(Author, date)", not like e.g. [1], etc.
+- Listing references that were not cited in text.
+- Using "et al." in the list of references. "et al." is used in in-text citations, but you must provide the full list of authors in the list of references (i.e. do not use "et al." here).
 
 # Spelling