doc: Typo train

Context

This is the "typo train", a batch of small, non-controversial changes to the documentation, aiming to minimize the overhead for tiny contributions.

Besides pure typos, there are the following simple changes:

• at the end of the script for compiling Tezos, invoke the node to detect missing zcash parameters
• upgrade Tezos binary installation scripts from 007 to 008 (for Ubuntu and Fedora)
• add a few page redirects for 007 doc pages
• fix path for contract id.tz (Issue #1168 (closed))
• mention the comment block at top of file also in Coding guidelines (was only mentioned in Contributing guidelines, when it is modified)
• print info about TEZOS_CLIENT_DIR env var in client --help (Issue #1162 (closed))

Manually testing the MR

Reviewers and approvers can test this MR by just checking that the changes are minor, non-controversial, and doing no harm (and ideally, doing some good!).

Checklist

section of CHANGES.md for everything else).

• Select suitable reviewers using the Reviewers field below.