Flesh out README

README.md

@@ -1,3 +1,44 @@
 # gg
 
 Recursive grep written in Go, for everyday ease of use.
+
+`gg` is a recursive grep. Given a regexp (or fixed pattern) it will search for
+the pattern recursively in the current working directory. It will print a
+coloured header per file along with the matching line and pattern.
+
+It is possible to scan specific files or directories, rather than the default
+current working directory. To do this, simply specify the path(s) as arguments
+following the pattern.
+
+It is possible to scan for multiple patterns using the `-e` (or `-Q`) argument,
+which can be repeated multiple times. `-e` specifies a regular expression and
+`-Q` a fixed pattern. When using either flag, any non-flag arguments are treated
+as paths to scan.
+
+Search defaults to case-sensitive but the `-i` flag may be passed to make all
+search terms case-insensitive. Alternatively, the `"(?i)"` construct may be added
+to a regular expression to make that specific expression case insensitive.
+
+Files and directories can be excluded with the `-x` option. This supports bash-style
+globs with `'*'`, `'?'`, `'[a-z]'`, `'{this,that}'`, or `'/**/'` to match zero or more
+directories. By default, `.git` and vim swap files are ignored. Similarly, `-I`
+filters files to include. Examples:
+
+```
+	# ignore files/dirs with .js or .css suffix
+	gg -x '*.js' -x '*.css' pattern
+
+	# only match files with .go suffix (any subdir)
+	gg -I '*.go' pattern
+
+	# only match files whose parent dir is "stuff", but ignore "foo" subdir
+	gg -x ./foo -I 'stuff/*' pattern
+
+	# only match .js files with a directory "things" in the path, but ignore
+	# .min.js (e.g. will match "foo/things/bar/my.js")
+	gg -I 'things/**/*.js' -x '*.min.js' pattern
+```
+
+Symlinks named on the command line are followed, but by default symlinks are
+not followed when recursing into directories. `-L` allows them to be
+dereferenced.