Update README for examples

Author: asottile

README.md

@@ -38,4 +38,26 @@ setup(
 
 ## Writing cpython extensions in golang
 
-TODO
+Here's some [examples](https://github.com/asottile/setuptools-golang-examples)
+
+## Common issues
+
+### `undefined reference to \`some_c_function'`
+
+`Extension` by default will bring along the go files listed, but won't bring
+along the related C files.  Add the following to `MANIFEST.in`:
+
+```
+global-include *.c
+global-include *.go
+```
+
+### `fatal: could not read Username for 'https://github.com':`
+
+You're probably trying to import from an external source which does not exist.
+Double check that your import is correct.
+
+
+### `package github.com/a/b/c: /tmp/.../github.com/a/b exists but /tmp/.../github.com/a/b/.git does not - stale checkout?`
+
+You've probably mistyped an import.  Double check that your import is correct.