Add new documentation for homebrew tap

Author: NlightNFotis

doc/ADR/README.md

@@ -9,3 +9,4 @@ of the system and the surrounding infrastructure.
 ## Release & Packaging
 
 * [Release Process](release_process.md)
+* [Homebrew tap](homebrew_tap.md)

doc/ADR/homebrew_tap.md

@@ -0,0 +1,71 @@
+# Homebrew tap instructions
+
+## User instructions
+
+1. Add the CBMC tap using the following command:
+
+   ```sh
+   $ brew tap diffblue/cbmc
+   ```
+
+2. Install any of the available CBMC versions in the following manner:
+
+   ```sh
+   $ brew install diffblue/cbmc/[email protected]
+   ```
+
+## Developer instructions
+
+1. First of all, you need to create a new tap locally:
+
+   ```sh
+   $ brew tap-new diffblue/homebrew-cbmc
+   ```
+
+   This step is needed if you are the one creating the tap.
+   If you want to install the tap that's already available
+   at the [Diffblue repository](https://github.com/diffblue/homebrew-cbmc),
+   `$ brew tap diffblue/cbmc` should suffice.
+
+
+2. For any edit, the second step is to `cd` into the repository.
+   To do that easily, it's best to ask Homebrew to give you the
+   location of the repository:
+
+   ```sh
+   $ cd $(brew --repo diffblue/cbmc)
+   ```
+
+3. You can extract versions of CBMC previously available in `homebrew/core` 
+   to the tap with the following instruction:
+
+   ```sh
+   $ brew extract cbmc diffblue/cbmc --version=<ver>
+   ```
+
+   For example `$ brew extract cbmc diffblue/cbmc --version=5.54.0` will
+   have as an end result a new file under `Formula/[email protected]` that will
+   contain the formula that we had submitted for that version of CBMC in the
+   `homebrew/core` repository.
+
+
+## Notes
+
+* Bootstrapping the repository with `brew tap --new` created two github actions
+  `.github/workflows/publish.yml` and `.github/workflows/tests.yml` which we are
+  not using at the moment but could serve to make future automation easier.
+
+## Known Limitations
+
+* The binaries are installed without any version tag attached, so they cannot
+  live side by side.
+* The install formula doesn't override binaries, so if you already have a CBMC
+  version installed, you need to `remove` it before installing another one:
+
+  ```sh
+  $ brew install diffblue/cbmc/[email protected]
+  [...]
+  $ brew remove [email protected]
+  [...]
+  $ brew install diffblue/cbmc/[email protected]
+  ```