Update conv.md

[itsmohitanand]

added GMMConv documentation

[CarloLucibello]

There is also a bunch of displaying issues in the docstring that you could fix in this PR

https://carlolucibello.github.io/GraphNeuralNetworks.jl/dev/api/conv/#GraphNeuralNetworks.GMMConv

[codecov]

Codecov Report

Merging #148 (5a3f40d) into master (8eddb5f) will not change coverage.
The diff coverage is n/a.

❗ Current head 5a3f40d differs from pull request most recent head a8166f1. Consider uploading reports for the commit a8166f1 to get more accurate results

@@           Coverage Diff           @@
##           master     #148   +/-   ##
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  Coverage   85.52%   85.52%           
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  Files          15       15           
  Lines        1285     1285           
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  Hits         1099     1099           
  Misses        186      186           

Impacted Files	Coverage Δ
src/layers/conv.jl	78.70% <ø> (ø)

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[CarloLucibello]

#Examples -> # Examples