DOC cleanup FAQ entry about Splash crashes

[kmike]

• fix ReST syntax (code-block was raising a syntax error because of
  a wrong indentation);
• move IndexedDB link to a previous section, where it is used;
• wording;
• mention Splash crashes caused by Splash bugs.

[codecov]

Codecov Report

Merging #878 into master will decrease coverage by 1.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #878      +/-   ##
==========================================
- Coverage   89.08%   87.66%   -1.42%     
==========================================
  Files          41       41              
  Lines        5725     5725              
  Branches      791      791              
==========================================
- Hits         5100     5019      -81     
- Misses        452      525      +73     
- Partials      173      181       +8

Impacted Files	Coverage Δ
splash/kernel/__main__.py	0% <0%> (-66.67%)	⬇️
splash/kernel/kernelbase.py	20.58% <0%> (-27.95%)	⬇️
splash/kernel/kernel.py	33.33% <0%> (-20.41%)	⬇️
splash/kernel/completer.py	88.31% <0%> (-7.8%)	⬇️
splash/server.py	75% <0%> (-5.44%)	⬇️
splash/qtutils.py	79.73% <0%> (-1.97%)	⬇️
splash/browser_tab.py	93.13% <0%> (-0.8%)	⬇️
splash/network_manager.py	84.33% <0%> (-0.34%)	⬇️
splash/qtrender_lua.py	95.64% <0%> (-0.16%)	⬇️