Added Note about arm7 version to doc

[suisseWalter]

This pull request adds a troubleshooting subsection for the non working arm7 release on raspberry Pi's in the installation part of the documentation.
This pull request was suggested in issue #6979

[mrsdizzie]

This feels wrong -- I still think we should just remove the arm7 version from the downloads section if it is known to not work for a while (and reported regularly). It doesn't make sense to offer something known to not work with a note that says "this does not work" buried in one of the docs.

Not fault of PR as it was suggested, but I think a better solution is to not give people a chance to download the file at all if we know it is broken, 100% avoiding the problem until it can be fixed.

[suisseWalter]

yes, I do agree with that but I don't have any idea on how to change that. therefore I did this. so if someone just removes arm7 I would be really happy. also is arm7 completely broken or only on raspbian?

[codecov-io]

Codecov Report

Merging #6983 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6983      +/-   ##
==========================================
- Coverage   41.49%   41.49%   -0.01%     
==========================================
  Files         440      440              
  Lines       59457    59457              
==========================================
- Hits        24672    24671       -1     
- Misses      31566    31567       +1     
  Partials     3219     3219

Impacted Files	Coverage Δ
routers/repo/view.go	42.02% <0%> (-1.02%)	⬇️
models/repo_list.go	73.09% <0%> (+1.01%)	⬆️
modules/log/colors_router.go	87.5% <0%> (+4.16%)	⬆️

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[lunny]

I like @mrsdizzie 's idea. We can manually delete exist arm-7 binaries and change the Makefile to avoid to compile arm7 binary.

[lafriks]

imho it is good to have info in docs while we have not fixed the issue

[zeripath]

@suisseWalter if you accept my suggested changes I'll approve. Even if we stop building the broken arm 7 builds we'll need to say something and this would do.

[zeripath]

make LG-TM work