Improve install instructions for Linux Mint

[thornjad]

fix #6446

The lsb_release method doesn't work for Mint since it's not
explicitly supported. This adds instructions for using the upstream
Ubuntu name instead.

Also a couple of formatting changes (no content change), and the word Brave was capitalized.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
  • Unsupported apt flavors return 403 #6446
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
  • see below
• Ran git rebase -i to squash commits (if needed).
  • not needed
• Tagged reviewers and labelled the pull request as needed.

Test Plan:

Since this is a text documentation file only, I didn't run any tests. If there are some to run, please let me know, I'd be happy run them.

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[posix4e]

Looks good at first glance. Thanks for doing this BTW. I assume you only tested one version? It's an improvement either way

[thornjad]

Correct, I only tested for Sonya, but I can run through a couple others if you like.

[posix4e]

It's always good to know which ones work. I'm always surprised + I will give you a shoutout on the blog post I am releasing.

[thornjad]

I'll give a few a run through! I'm surely no stranger to surprises in the least expected places. Do you think one test per Ubuntu base should be enough? Say, Sonya, Rosa and Betsy?

[posix4e]

@Raindeer44 Because of my usual habits we get good coverage on 14,16 and 17. I also test and verify that I can build on Debian testing generally

[thornjad]

@posix4e I can do 16, 17 and LMDE for sure, but I don't have 14 available off-hand and I'd have to track down the ISO for a VM. Regular Debian should still work with the lsb_release method, I believe

[posix4e]

@Raindeer44 OOh I mean I test ubuntu 14 lts, 16 lts and whatever new 17 is

[thornjad]

@posix4e OHHH yeah, that makes a lot of sense. Mint is based on Ubuntu's LTS's so then testing Mint 17 and 18 (Ubuntu 14 and 16) should cover it, plus LMDE for good measure.

[codecov-io]

Codecov Report

Merging #11241 into master will decrease coverage by 2.85%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11241      +/-   ##
==========================================
- Coverage   54.32%   51.47%   -2.86%     
==========================================
  Files         255      263       +8     
  Lines       22070    25484    +3414     
  Branches     3446     4310     +864     
==========================================
+ Hits        11990    13117    +1127     
- Misses      10080    12367    +2287

Flag	Coverage Δ
#unittest	51.47% <ø> (-2.86%)	⬇️

Impacted Files	Coverage Δ
app/common/state/siteSettingsState.js	71.42% <0%> (-19.49%)	⬇️
.../renderer/components/navigation/publisherToggle.js	94.8% <0%> (-3.56%)	⬇️
...r/components/preferences/payment/ledgerRecovery.js	32.46% <0%> (-2.02%)	⬇️
js/about/aboutActions.js	9.3% <0%> (-1.99%)	⬇️
...r/components/preferences/payment/enabledContent.js	92.77% <0%> (-1.3%)	⬇️
...pp/renderer/components/navigation/navigationBar.js	97.89% <0%> (-0.83%)	⬇️
js/actions/appActions.js	12.47% <0%> (-0.45%)	⬇️
js/constants/messages.js	100% <0%> (ø)	⬆️
js/constants/appConstants.js	100% <0%> (ø)	⬆️
js/constants/stateConstants.js	100% <0%> (ø)	⬆️
... and 18 more

[thornjad]

To be clear (just in case), I did successfully test these changed instructions on Linux Mint 17, 18 and LMDE 2 👍