README: add styleguide section

README.md

@@ -12,3 +12,24 @@ Other third-party packages which integrate into these:
   package has a specific error it might return and which might be checked for a
   function to perform that equality check will be supplied as part of the
   package.
+
+## Styleguide
+
+Here are general guidelines I use when making decisions about how code in this
+repo should be written. Most of the guidelines I have come up with myself have
+to do with package design, since packages are the only thing which have any
+rigidity and therefore need any rigid rules.
+
+Everything here are guidelines, not actual rules.
+
+* `gofmt -s`
+
+* https://golang.org/doc/effective_go.html
+
+* https://github.com/golang/go/wiki/CodeReviewComments
+
+* When deciding if a package should initialize a struct as a value or pointer, a
+  good rule is: If it's used as an immutable value it should be a value,
+  otherwise it's a pointer. Even if the immutable value implementation has
+  internal caching, locks, etc..., that can be hidden as pointers inside the
+  struct, but the struct itself can remain a value type.