Expand macOS docs for core homebrew formula

I'm working on a formula for the core Homebrew repository that would
support all but Firebird and Oracle. So highlight it here, and document
the installation of additional libraries. The Homebrew formula will link
to this page when installation finishes.

But also cover the tap for those who need to manage Oracle or Firebird
databases.

content/download/macos.md

@@ -6,22 +6,115 @@ id: install
 
 {{% section class="brew" %}}
 
-The [Sqitch Homebrew Tap] quickly builds Sqitch on your Mac. To install from
-Homebrew, configure the tap and then install the variants you need via the
-appropriate `--use-$engine-support` options. For example, to install Sqitch with
-[PostgreSQL] and [SQLite] support:
+There are two methods to quickly install Sqitch on macOS using [Homebrew]. Use
+the [Sqitch Homebrew formula] to manage [PostgreSQL], [SQLite], and [MySQL]
+databases. It can also manage [Vertica], [Exasol], and [Snowflake] databases
+with the installation of additional client libraries, described below.
 
-    brew tap sqitchers/sqitch
-    brew install sqitch --with-postgres-support --with-sqlite-support
+``` sh
+brew install sqitch
+```
 
-Some engines require the installation of dependencies in advance; consult [the
-docs] for build details and options.
+Use the [Sqitch Homebrew Tap] to manage [Oracle] or [Firebird] databases, as
+detailed below.
 
+### Postgres, SQLite, MySQL
+
+The [Sqitch Homebrew formula] installs all the libraries needed to manage
+[SQLite], [MySQL], [MariaDB], [PostgreSQL], [YugabyteDB], and [CockroachDB]
+databases.
+
+### Vertica
+
+To manage [Vertica] databases, Sqitch depends on the presence of the Vertica
+ODBC driver and the `vsql` client. [Download][vsql] and install the ODBC and
+`vsql` packages for macOS prior to using Sqitch to manage Vertica databases.
+
+### Exasol
+
+To manage [Exasol] databases, Sqitch depends on the presence of the Exasol ODBC
+driver and the `EXAplus` client. [Download][exaplus] and install the ODBC and
+`EXAplus` packages for macOS prior to using Sqitch to manage Exasol databases.
+
+### Snowflake
+
+To manage [Snowflake] databases, Sqitch depends on the presence of the Snowflake
+ODBC driver (the `snowsql` client is installed by Homebrew). Download
+and install the [Snowflake ODBC driver] macOS prior to using Sqitch to manage
+Snowflake databases.
+
+### Firebird
+
+Use the [Sqitch Homebrew Tap] to manage [Firebird] databases. It depends on the
+presence of a Firebird database installation, both to build the necessary
+database driver at build time, and to use the `isql` client to manage databases
+at runtime. Alas, there appears to be no Homebrew formula for Firebird, so
+you'll have to manually [download][fbsql] and install it, then install Sqitch
+from the tap like so:
+
+``` sh
+brew tap sqitchers/sqitch
+brew install sqitch --with-firebird-support
+```
+If no Firebird driver library is found, the build will fail.
+
+### Oracle
+
+Use the [Sqitch Homebrew Tap] to manage [Oracle] databases. This feature depends
+on the presence of the [Oracle Instant Client] Basic and SDK packages to build
+the necessary database driver at build time, plus the SQL\*Plus package to
+manage databases at runtime. If no Instant Client files are found, the build
+will fail.
+
+Sadly, [System Integrity Protection] must be disabled in order to build Sqitch
+with Oracle support. This is to allow the setting of the `$DYLD_LIBRARY_PATH`
+environment variable, which is required for Oracle support in Sqitch. [Here's
+how].
+
+With SIP disabled, set `$HOMEBREW_ORACLE_HOME` to the full path to the directory
+for Instant Client. This will allow the build to find the libraries necessary to
+complete the build with Oracle support. To use Sqitch with Oracle, you will
+need to set the `$ORACLE_HOME` and `$DYLD_LIBRARY_PATH` variables to point to
+the Instant Client, something like:
+
+``` sh
+export ORACLE_HOME=/usr/local/instantclient_12_2
+export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:$ORACLE_HOME
+brew install sqitch --with-oracle-support
+```
+
+  [Homebrew]: https://brew.sh "The Missing Package Manager for macOS"
+  [Sqitch Homebrew formula]: https://formulae.brew.sh/formula/sqitch
+    "Sqitch Homebrew Formula"
   [Sqitch Homebrew Tap]: https://github.com/sqitchers/homebrew-sqitch/
   [PostgreSQL]: https://postgresql.org/
     "PostgreSQL: The World's Most Advanced Open Source Relational Database"
   [SQLite]: https://sqlite.org/
     "SQLite: Small. Fast. Reliable. Choose any three."
   [the docs]: https://github.com/sqitchers/homebrew-sqitch/#readme
+  [Vertica]: https://www.vertica.com/ "Vertica Analytics Platform"
+  [Exasol]: https://www.exasol.com/ "Exasol: The In-Memory Database Built for Analytics"
+  [Snowflake]: https://www.snowflake.com/ "Snowflake: The Data Cloud"
+  [vsql]: https://www.vertica.com/download/vertica/client-drivers/
+    "Vertica Downloads: Client Drivers"
+  [exaplus]: https://downloads.exasol.com "Exasol Downloads"
+  [Snowflake ODBC driver]: https://docs.snowflake.net/manuals/user-guide/odbc-download.html
+   "Snowflake Documentation: “Downloading the ODBC Driver”"
+  [Oracle]: https://www.oracle.com/database/ "Oracle Database"
+  [Firebird]: https://www.firebirdsql.org "Firebird open source database"
+  [fbsql]: https://www.firebirdsql.org/en/server-packages/
+    "Firebird Server Packages"
+  [Oracle Instant Client]: https://www.oracle.com/technetwork/topics/intel-macsoft-096467.html
+    "Oracle Instant Client Downloads for macOS"
+  [System Integrity Protection]: https://support.apple.com/en-us/HT204899
+    "About System Integrity Protection on your Mac"
+  [Here's how]: https://www.imore.com/how-turn-system-integrity-protection-macos
+    "iMore: “How to turn off System Integrity Protection on your Mac”"
+  [MySQL]: https://www.mysql.com "MySQL: The world's most popular open source database"
+  [MariaDB]: https://mariadb.org "MariaDB Server: The open source relational database"
+  [YugabyteDB]: https://www.yugabyte.com/yugabytedb/
+    "YugabyteDB: The open source distributed SQL database for cloud native transactional applications"
+  [CockroachDB]: https://www.cockroachlabs.com/product/
+    "CockroachDB: The world’s most evolved cloud SQL database"
 
-{{% /section %}}
+{{% /section %}}