archlinux: shorten sentence

Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217320
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
archlinux: fix 2 sentences

Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217322
Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217323
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
enterprise: define acronyms RHEL and SLES

Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217354
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
getting-started: fix formatting in tracing paragraph

Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217394
Link: https://github.com/lttng/lttng-docs/pull/3#commitcomment-8217401
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>