Merge #19124: doc: Document ALLOW_HOST_PACKAGES dependency option

47e2a35fac doc: Document ALLOW_HOST_PACKAGES dependency option (skmcontrib)

Pull request description:

  Provided entry in depends, README.md to ensure that ALLOW_HOST_PACKAGES dependency option is documented, #19113

ACKs for top commit:
  hebasto:
    ACK 47e2a35fac.

Tree-SHA512: 10d9285885be25f092881e4886c6a804cd42b5224bdf1dfa8b8369463808ddaf533a8604f14f7fe45478434a22feae98053f4731b51d976c071d69882bdac72b

depends/README.md

@@ -105,6 +105,10 @@ The following can be set when running make: `make FOO=bar`
 <dd>Don't download/build/cache SQLite</dd>
 <dt>NO_UPNP</dt>
 <dd>Don't download/build/cache packages needed for enabling upnp</dd>
+<dt>ALLOW_HOST_PACKAGES</dt>
+<dd>Packages that are missed in dependencies (due to `NO_*` option or
+build script logic) are searched for among the host system packages using
+`pkg-config`. It allows building with packages of other (newer) versions</dd>
 <dt>MULTIPROCESS</dt>
 <dd>build libmultiprocess (experimental, requires cmake)</dd>
 <dt>DEBUG</dt>