doc/pkg-config: add instructions about custom pkg-config files

.gitignore

@@ -7,6 +7,9 @@ container-build-cache/
 # local genbindings configuration
 cmd/genbindings/genbindings.local*
 
+# local pkg-config configuration
+pkg-config/*.pc
+
 # binaries
 cmd/handbindings/handbindings
 cmd/handbindings/bindings_test/direct

pkg-config/README.md

@@ -0,0 +1,27 @@
+# pkg-config
+
+MIQT always uses [pkg-config](https://people.freedesktop.org/~dbn/pkg-config-guide.html) to find C++ libraries to bind to.
+
+For Qt Widgets, the `.pc` definition is supplied along with Qt, but for other third-party libraries, definitions might not be present. To use such third-party libraries, one option is to set the `CGO_CFLAGS`, `CGO_CXXFLAGS`, `CGO_LDFLAGS` environment variables for `go build`. However, this has a global effect and may cause issues if you use multiple libraries. Therefore, another option is to create a pkg-config file.
+
+To specify the CFLAGS/CXXFLAGS and LDFLAGS for a specific library, make a `MyLibrary.pc` file as follows:
+
+```pkgconfig
+Name: My Library
+Libs: -lfoo
+Cflags: -I/path/
+```
+
+Then run `PKG_CONFIG_PATH=/path/to/dir/ go build` so CGO will find your library. Then, the necessary flags for your system will be used only as required for the specific package.
+
+The `PKG_CONFIG_PATH` environment variable is understood both by CGO and by genbindings.
+
+## Further reading
+
+- [Guide to pkg-config](https://people.freedesktop.org/~dbn/pkg-config-guide.html)
+
+```bash
+# Find where pkg-config looks for system libraries
+$ pkg-config --variable pc_path pkg-config
+/usr/local/lib/x86_64-linux-gnu/pkgconfig:/usr/local/lib/pkgconfig:/usr/local/share/pkgconfig:/usr/lib/x86_64-linux-gnu/pkgconfig:/usr/lib/pkgconfig:/usr/share/pkgconfig
+```