Merge #18070: doc: add note about brew doctor

63ce882 doc: link to homebrew's troubleshooting page (Gastón I. Silva)

Pull request description:

  A trivial documentation update.

  When I was following the build steps for mac, I had some errors installing the dependencies. After searching on the Internet, and correcting the errors, I found that `brew doctor` had all the answers I needed. Could have skipped the Internet searches all together.

ACKs for top commit:
  fanquake:
    ACK 63ce882 - a link to the troubleshooting page seems fine. I wouldn't really want our README to have anything more specific than that.

Tree-SHA512: 12c96cd9c9bd39ada21f3f27cbec3ed4bef4b8e74dec7872c892fc6a92a70418a5cc0882ff449883e91d96c01e1ca7104b076590917f397334c82931ec7fda1c

Author: fanquake

doc/build-osx.md

@@ -22,6 +22,7 @@ Then install [Homebrew](https://brew.sh).
 brew install automake berkeley-db4 libtool boost miniupnpc pkg-config python qt libevent qrencode
 ```
 
+If you run into issues, check [Homebrew's troubleshooting page](https://docs.brew.sh/Troubleshooting).
 See [dependencies.md](dependencies.md) for a complete overview.
 
 If you want to build the disk image with `make deploy` (.dmg / optional), you need RSVG: