Consolidate Library READMEs with installation tutorials

[chapulina]

Some libraries have repeated content in their installation tutorials and READMEs
Choose one or the other for each library to have

[ahcorde]

Consolidated install documentation for the following libraries (Moved install instructions to the tutorials folder):

• ign-fuel-tools Removed repeated installation instructions gz-fuel-tools#101
• ign-gui Removed repeated installation instructions gz-gui#106
• ign-math Removed repeated installation instructions gz-math#147
• ign-physics Removed repeated installation instructions gz-physics#95
• ign-plugin Removed repeated installation instructions gz-plugin#27
• ign-rendering Removed repeated installation instructions gz-rendering#125
• ign-transport Removed repeated installation instructions gz-transport#160

[chapulina]

Thanks for taking this on, @ahcorde !

I commented on one of the PRs, but for completeness I'll mention it here too that we should be linking to the published link of those installation tutorials, such as

https://ignitionrobotics.org/api/math/6.4/install.html

The reasons are:

• The READMEs are rendered not only on GitHub but also (once Fix READMEs and Changelogs not rendering on /libs/libname #58 is fixed) on pages like this, and relative links to the tutorials won't work: https://ignitionrobotics.org/libs/math
• The tutorials may not always render correctly on GitHub, their canonical location is on the ignitionrobotics.org site

[chapulina]

Reopening as we're still missing some libraries:

• ign-cmake (note that its tutorials aren't being deployed yet, see Missing libs on docs page #53)
• ign-common
• ign-tools (this one is tricky, because it doesn't use ign-cmake, so Missing libs on docs page #53 is also tricky)
• ign-gazebo
• ign-msgs
• ign-launch