[R-390] Added link to 'Short Wave' magazines to website

[Larry H]

I added a link to the 'Short Wave' magazines to our website at the top of
the 'Magazines' section of the 'References' page.  Here's a link to the
'Magazines' section: The R-390A 'Magazines' section
<https://www.r-390a.net/faq-refs.htm#Magazines>.

I also added a link to an improved copy of the EAC Ad for an R-390A in the
73 Magazine in the 'Other Tutorials' section of the 'References' page.
Here's a link to the Ad: R-390A 73 Magazine Ad 12-1968 p70
<https://www.r-390a.net/R390A%2073%20Mag%20Ad%2012-1968%20p70.png>.

Regards, Larry