Docs(README): Fix example configuration

As mentioned in #23, the TOML was invalid in multiple ways. It should
now be a bit better.

Signed-off-by: Paul Mabileau <paul.mabileau@harfanglab.fr>

README.md

@@ -672,11 +672,12 @@ properly-formed TOML document respecting the following format:
 [packages]
 package-name-1 = "version-req-1"
 package-name-2 = "version-req-2"
-package-name-3 = {
-    version = "version-req-3",
-    all-features = boolean,
-    default-features = boolean,
-    features = ["feature-1", "feature-2"],
+
+    [packages.package-name-3]
+    version = "version-req-3"
+    all-features = boolean
+    default-features = boolean
+    features = ["feature-1", "feature-2"]
     index = "http://example.com/"
     registry = "example-registry"
     git = "http://example.com/exa/mple.git"
@@ -693,9 +694,8 @@ package-name-3 = {
     frozen = boolean
     locked = boolean
     offline = boolean
-    extra-arguments = ["--arg1", "--arg2"],
-    environment = { ENV1 = "abc", ENV2 = "def" },
-}
+    extra-arguments = ["--arg1", "--arg2"]
+    environment = { ENV1 = "abc", ENV2 = "def" }
 #...
 ```