docs: update README and Makefile with a few more build examples

Makefile

@@ -19,7 +19,7 @@ libhydrogen-clean:
 	make -C libhydrogen clean
 
 ################################################################################
-.PHONY: fmt run test
+.PHONY: fmt run test run_custom_ld rerun
 fmt:
 	$(SHELL) scripts/cmd.sh "fmt"
 
@@ -29,6 +29,11 @@ test:
 run:
 	env CGO_ENABLED=1 go run tests/main.go
 
+run_custom_ld:
+	env CGO_ENABLED=1 CGO_LDFLAGS="-L/path/to/libhydrogen" CGO_CFLAGS="-I/path/to/libhydrogen" go run tests/main.go
+
+rerun:
+	env CGO_ENABLED=1 go run -a tests/main.go
 ################################################################################
 .PHONY: race
 race:

README.md

@@ -5,25 +5,61 @@ Golang wrapper for [libhydrogen](https://github.com/jedisct1/libhydrogen).
 ## Usage
 
 If libhydrogen is already installed system-wide, just `go get` the project
-and import `libhydrogen-go` like anything else. Otherwise, you may build
-`libhydrogen.a` inside the submodule directory.
+and import `libhydrogen-go` like anything else. Otherwise, you may build and
+install `libhydrogen.a` from the submodule directory.
+
+**Note**: `libhydrogen-go` is only tested to work against the version of
+libhydrogen included as a submodule in this repo.
+
+**Specifying libhydrogen location**: See the `make run_custom_ld` target in
+Makefile for example.
+
+**Note**: If editing / recompiling `libhydrogen` and then running tests, it may
+be necessary to build with the `-a` flag to force a rebuild. See `make rebuild`
+target in Makefile for example.
 
 ```sh
+# add as go mod dependency
 go get github.com/someburner/libhydrogen-go
+```
+<br>
+
+```go
+// and use in project
+package main
+
+import (
+	"fmt"
+	hydro "github.com/someburner/libhydrogen-go"
+)
+
+func main() {
+	fmt.Println(hydro.VersionVerbose())
+}
+```
+
+## Install libhydrogen
 
+```sh
 # to build inside submodule, or run the examples
-cd github.com/someburner/libhydrogen-go
-make libhydrogen
+git clone --recursive https://github.com/someburner/libhydrogen-go.git
+cd libhydrogen-go
 
-# go run tests/main.go
-make run
+# build/install libhydrogen
+cd libhydrogen
+make
+sudo make install
 ```
 
 <br>
 
 ## Examples
 
-See [example](tests/main.go).
+See [example](tests/main.go). Or run with `make`.
+
+```sh
+make run
+```
 
 ## Links