write changelog for v0.3.0

While writing it, I also noticed that the second change for #73,
where we now separate ") {" even if there's no empty line,
wasn't documented in the README. It now is.

CHANGELOG.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## [0.3.0] - 2022-02-22
+
+This is gofumpt's third major release, based on Go 1.18's gofmt.
+The jump from Go 1.17's gofmt should bring a noticeable speed-up,
+as the tool can now format many files concurrently.
+On an 8-core laptop, formatting a large codebase is 4x as fast.
+
+The following [formatting rules](https://github.com/mvdan/gofumpt#Added-rules) are added:
+
+* Functions should separate `) {` where the indentation helps readability
+* Field lists should not have leading or trailing empty lines
+
+The following changes are included as well:
+
+* Generated files are now fully formatted when given as explicit arguments
+* Prepare for Go 1.18's module workspaces, which could cause errors
+* Import paths sharing a prefix with the current module path are no longer
+  grouped with standard library imports
+* `format.Options` gains a `ModulePath` field per the last bullet point
+
 ## [0.2.1] - 2021-12-12
 
 This bugfix release resolves a number of issues:

README.md

@@ -63,13 +63,19 @@ func foo() {
 
 </details>
 
-Functions using an empty line for readability should use a `) {` line instead
+Functions should separate `) {` where the indentation helps readability
 
 <details><summary><i>example</i></summary>
 
 ```
 func foo(s string,
 	i int) {
+	println("bar")
+}
+
+// With an empty line it's slightly better, but still not great.
+func bar(s string,
+	i int) {
 
 	println("bar")
 }
@@ -81,6 +87,13 @@ func foo(s string,
 ) {
 	println("bar")
 }
+
+// With an empty line it's slightly better, but still not great.
+func bar(s string,
+	i int,
+) {
+	println("bar")
+}
 ```
 
 </details>