Update README with apply status

Author: bluekeyes

README.md

@@ -6,7 +6,8 @@ A Go library for parsing and applying patches generated by `git diff`, `git
 show`, and `git format-patch`. It can also parse and apply unified diffs
 generated by the standard `diff` tool.
 
-It supports both standard line-oriented text patches and Git binary patches.
+It supports standard line-oriented text patches and Git binary patches, and
+aims to parse anything accepted by the `git apply` command.
 
 ```golang
 patch, err := os.Open("changes.patch")
@@ -23,11 +24,11 @@ if err != nil {
 // preamble is a string of the content of the patch before the first file
 ```
 
-## Status
+## Development Status
 
-In development, expect API changes. Patch parsing works, but has not been
-tested extensively against real-world patches. Patch application has not been
-implemented yet.
+Mostly complete, but API changes are possible. Patch parsing and strict
+application works and is well-covered by unit tests, but has not been validated
+extensively against real-world patches.
 
 ## Why another git/unified diff parser?
 
@@ -75,3 +76,8 @@ implemented yet.
 5. When reading "traditional" patches (those not produced by `git`), prefixes
    are not stripped from file names; `git apply` attempts to remove prefixes
    that match the current repository directory/prefix.
+
+6. Patches can only be applied in "strict" mode, where the line numbers and
+   context of each fragment must exactly match the source file; `git apply`
+   implements a search algorithm that tries different lines and amounts of
+   context, with further options to normalize or ignore whitespace changes.