Fix the pages in the manual for Lix

This doesn't comprehensively fix everything outdated in the manual, or
make the manual greatly better, but it does note down where at least
jade noticed it was wrong, and it does fix all the instances of
referencing Nix to conform to the style guide to the best of our
ability.

A lot of things have been commented out for being wrong, and there are
three types of FIXME introduced:

- FIXME(Lix): generically Lix needs to fix it
- FIXME(Qyriad): re https://git.lix.systems/lix-project/lix/issues/215
- FIXME(meson): docs got outdated by meson changes and need rewriting

I did fix a bunch of it that I could, but there could certainly be
mistakes and this is definitely just an incremental improvement.

Fixes: https://git.lix.systems/lix-project/lix/issues/266
Change-Id: I5993c4603d7f026a887089fce77db08394362135

doc/manual/src/installation/installing-binary.md

@@ -1,5 +1,11 @@
 # Installing a Binary Distribution
 
+See https://lix.systems/install/ for more details.
+
+<!--
+
+FIXME(Lix): There are a bunch of technical details on *how* nix is installed in here that we want to keep but it would need serious rewriting.
+
 The easiest way to install Nix is to run the following command:
 
 ```console
@@ -81,7 +87,7 @@ extension. The installer will also create `/etc/profile.d/nix.sh`.
 # macOS Installation
 
 []{#sect-macos-installation-change-store-prefix}[]{#sect-macos-installation-encrypted-volume}[]{#sect-macos-installation-symlink}[]{#sect-macos-installation-recommended-notes}
-<!-- Note: anchors above to catch permalinks to old explanations -->
+<!~~ Note: anchors above to catch permalinks to old explanations ~~>
 
 We believe we have ironed out how to cleanly support the read-only root
 on modern macOS. New installs will do this automatically.
@@ -101,7 +107,7 @@ this to run the installer, but it may help if you run into trouble:
   - `nobrowse`: prevent the Nix Store volume from showing up on your
     desktop; also keeps Spotlight from spending resources to index
     this volume
-  <!-- TODO:
+  <!~~ TODO:
   - `suid`: honor setuid? surely not? ...
   - `owners`: honor file ownership on the volume
 
@@ -117,7 +123,7 @@ this to run the installer, but it may help if you run into trouble:
     new reports from coming in. But I hesitate to celebrate because we
     haven't really named and catalogued the behavior, understood what
     we're fixing, and validated that all 3 components are essential.
-  -->
+  ~~>
 - if you have FileVault enabled
     - generate an encryption password
     - put it in your system Keychain
@@ -156,3 +162,5 @@ $ ./install
 If you need to edit the multi-user installation script to use different
 group ID or a different user ID range, modify the variables set in the
 file named `install-multi-user`.
+
+-->