Clarify manifest format docs for [badges] section

Previously the `[badges]` section documentation was mixed in with the
`[package]` section. This extracts it out under its own heading.

This also pulls the `license` and `license-file` field documentation out
of the package metadata code block. It sets the example license to “MIT
OR Apache-2.0” since that is the typical licensing scheme for many
crates.

This includes minor rewrites for clarity and to match the register of
the rest of the document.

This resolves issue rust-lang#7691.

src/doc/src/reference/manifest.md

@@ -221,6 +221,34 @@ workspace = "path/to/workspace/root"
 
 For more information, see the documentation for the workspace table below.
 
+#### The `license` and `license-file` fields (optional)
+
+The `license` field can be set to an [SPDX 2.1 license
+expression][spdx-2.1-license-expressions] for the package. Currently crates.io
+will validate the license provided against a whitelist of known license and
+exception identifiers from the [SPDX license list 3.6][spdx-license-list-3.6].
+Parentheses are not currently supported.
+
+Previously multiple licenses could be separated with a `/`, but that usage is
+deprecated. Instead, use a license expression with AND and OR operators to get
+more explicit semantics.
+
+```toml
+[package]
+# ...
+license = "MIT OR Apache-2.0"
+```
+
+If a package is using a nonstandard license, then the `license-file` field may
+be specified in lieu of the `license` field. It must point to a file relative to
+this manifest (similar to the `readme` field).
+
+```toml
+[package]
+# ...
+license-file = "..."
+```
+
 #### Package metadata
 
 There are a number of optional metadata fields also accepted under the
@@ -255,35 +283,31 @@ keywords = ["...", "..."]
 # Categories are a fixed list available at crates.io/category_slugs, and
 # they must match exactly.
 categories = ["...", "..."]
+```
 
-# This is an SPDX 2.1 license expression for this package. Currently
-# crates.io will validate the license provided against a whitelist of
-# known license and exception identifiers from the SPDX license list
-# 3.6. Parentheses are not currently supported.
-#
-# Multiple licenses can be separated with a `/`, although that usage
-# is deprecated. Instead, use a license expression with AND and OR
-# operators to get more explicit semantics.
-license = "..."
-
-# If a package is using a nonstandard license, then this key may be specified in
-# lieu of the above key and must point to a file relative to this manifest
-# (similar to the readme key).
-license-file = "..."
+The [crates.io](https://crates.io) registry will render the description, display
+the license, link to the three URLs and categorize by the keywords. These keys
+provide useful information to users of the registry and also influence the
+search ranking of a crate. It is highly discouraged to omit everything in a
+published crate.
+
+### The `[badges]` section
+
+crates.io can display various badges for build status, test coverage, etc. for
+each crate. All badges are optional.
+
+- The badges pertaining to build status that are currently available are
+  Appveyor, CircleCI, Cirrus CI, GitLab, Azure DevOps, Travis CI and Bitbucket
+  Pipelines.
+- Available badges pertaining to code test coverage are Codecov and Coveralls.
+- There are also maintenance-related badges based on isitmaintained.com
+  which state the issue resolution time, percent of open issues, and future
+  maintenance intentions.
+
+Most badge specifications require a `repository` key. It is expected to be in
+`user/repo` format.
 
-# Optional specification of badges to be displayed on crates.io.
-#
-# - The badges pertaining to build status that are currently available are
-#   Appveyor, CircleCI, Cirrus CI, GitLab, Azure DevOps, Travis CI and Bitbucket
-#   Pipelines.
-# - Available badges pertaining to code test coverage are Codecov and
-#   Coveralls.
-# - There are also maintenance-related badges based on isitmaintained.com
-#   which state the issue resolution time, percent of open issues, and future
-#   maintenance intentions.
-#
-# If a `repository` key is required, this refers to a repository in
-# `user/repo` format.
+```toml
 [badges]
 
 # Appveyor: `repository` is required. `branch` is optional; default is `master`
@@ -346,17 +370,6 @@ is-it-maintained-open-issues = { repository = "..." }
 maintenance = { status = "..." }
 ```
 
-The [crates.io](https://crates.io) registry will render the description, display
-the license, link to the three URLs and categorize by the keywords. These keys
-provide useful information to users of the registry and also influence the
-search ranking of a crate. It is highly discouraged to omit everything in a
-published crate.
-
-SPDX 2.1 license expressions are documented
-[here][spdx-2.1-license-expressions]. The current version of the
-license list is available [here][spdx-license-list], and version 3.6
-is available [here][spdx-license-list-3.6].
-
 #### The `metadata` table (optional)
 
 Cargo by default will warn about unused keys in `Cargo.toml` to assist in
@@ -946,4 +959,3 @@ dependencies][replace] section of the documentation.
 [`cargo test`]: ../commands/cargo-test.md
 [spdx-2.1-license-expressions]: https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60
 [spdx-license-list-3.6]: https://github.com/spdx/license-list-data/tree/v3.6
-[spdx-license-list]: https://spdx.org/licenses/