Update PR template

[tupaschoal]

I made most of the things comments, so contributors only have a guidance on what to write, but don't have to keep erasing stuff that was not applicable, like I did :D

I also suggested using "Closes #XXX" to make sure the PR closes the related issue and we don't have to keep doing housecleaning.

[codecov]

Codecov Report

Merging #264 into master will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
- Coverage   55.12%   55.08%   -0.05%     
==========================================
  Files          13       13              
  Lines        1219     1220       +1     
  Branches      217      218       +1     
==========================================
  Hits          672      672              
  Misses        480      480              
- Partials       67       68       +1     

Impacted Files	Coverage Δ
main.js	0.00% <0.00%> (ø)

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