The Daily Press article is included in the novel, in the section called "Progress Report 14," on June 15th of Charlie's diary, because it provides these details relevant to the plot:
1. It reveals that Charlie's sister Norma had been under the impression that Charlie was long since dead, and that now she hopes she can be reunited with him. This information is essential in helping Charlie forgive Norma and understand her perspective.
2. It reveals that Charlie's mother Rose had lied to everyone about Charlie being dead many years before. Though callous and depressing, this information helps Charlie understand where he stands with his mother.
3. It shows, in the description of the newspaper photograph, what Norma and Rose look like now. This is relevant because Charlie may not have been able to recognize them otherwise.
4. It indicates that Charlie's father, Matthew, runs a barbershop in a particular part of the city (the Bronx). This detail allows Charlie to seek out his father later on.
5. Most importantly, it reveals the address where Norma and Rose still live. Charlie will use this information to confront his mother.
In addition to providing the information above that allows the plot to move forward, the news article triggers more recollections in Charlie's mind when he views the photograph.
Finally, the news article also provides a bit of variety in the text, a quick break from the constant stream of descriptions from Charlie's perspective.