install docs: one subsection per OS

'With Homebrew (macOS or Linux)' followed by a source build made every
reader parse which half was theirs; now macOS and Linux each have a
heading, and you read yours. macOS is the tap; Linux is the same tap
under Homebrew on Linux, or the source build, which the docs landing
page had never mentioned brew at all.

Also fixes the README telling people to run bare 'make', which prints
the help text (the default goal) and builds nothing. install.sh had
this figured out and commented on it; the README had not.

1 files changed, 20 insertions, 2 deletions

diff --git a/docs/index.md b/docs/index.md
index e8a7bfd..587d47b 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -5,15 +5,33 @@ in C on top of [libghostty-vt](https://github.com/ghostty-org/ghostty).
 
 ## Install
 
-Needs [zig](https://ziglang.org) 0.16 and nothing else: no cmake, no
-autotools, no libraries. The result is one static binary.
+### macOS
+
+With [Homebrew](https://brew.sh):
+
+```bash
+brew tap sl0p/slosh https://git.sl0p.foo/homebrew-slosh.git
+brew install slosh
+```
+
+### Linux
+
+The same tap works under [Homebrew on
+Linux](https://docs.brew.sh/Homebrew-on-Linux), or build from source. That
+needs [zig](https://ziglang.org) 0.16 and nothing else: no cmake, no
+autotools, no libraries. The result is one static binary that runs on any
+distro.
 
 ```bash
 make vendor    # build the vendored terminal core (once, a couple of minutes)
 make all       # a few seconds
 make test      # optional: the whole suite, about thirteen seconds
+sudo make install
 ```
 
+(The source build works on a mac too; Homebrew is simply the shorter road
+there.)
+
 ## Run
 
 ```bash