Update README.md (#19551)

* Update README.md

Minor grammar and formatting changes.

Took a stab at adding an intro, feel free to improve.

* Update README.md

packaging/docker/README.md

 # Grafana Docker image
 
-## Running your Grafana container
+This topic contains instructions for installing Grafana using the Docker image.
 
-Start your container binding the external port `3000`.
+## Run the Grafana Docker container
+
+Start the Docker container by binding Grafana to external port `3000`.
 
 ```bash
 docker run -d --name=grafana -p 3000:3000 grafana/grafana
 ```
 
-Try it out, default admin user is admin/admin.
-
-## How to use the container
+Try it out, default admin user credentials are admin/admin.
 
-Further documentation can be found at http://docs.grafana.org/installation/docker/
+Further documentation can be found at http://docs.grafana.org/installation/docker/.
 
 ## Changelog
 
 ### v6.4.0-pre1
 
-* Switch base image from ubuntu:18.04 to alpine:3.10
+* Switched base image from Ubuntu:18.04 to Alpine:3.10.
 
 ### v6.3.0-beta2
-* Switch base image from ubuntu:latest to ubuntu:18.04
+* Switched base image from Ubuntu:latest to Ubuntu:18.04.
 
 ### v6.3.0-beta1
-* Switch base image to ubuntu:latest from debian:stretch to avoid security issues.
+* Switched base image to Ubuntu:latest from Debian:stretch to avoid security issues.
 
 ### v5.4.3
-* Build and publish docker images for armv7 and arm64 #14617, thx @johanneswuerbach
+* Added ability to build and publish Docker images for armv7 and arm64, #14617, thx @johanneswuerbach.
 
 ### v5.3.2
-* adds curl back into the docker image for utility. #13794
+* Added Curl back into the Docker image for utility, #13794.
 
 ### v5.3.0-beta1
-* Make it possible to set a specific plugin url #12861, thx ClementGautier
+* Made it possible to set a specific plugin URL, #12861, thx ClementGautier.
 
 ### v5.1.5, v5.2.0-beta2
-* Fix: config keys ending with _FILE are not respected [#170](https://github.com/grafana/grafana-docker/issues/170)
+* Fixed: config keys ending with _FILE are not respected [#170](https://github.com/grafana/grafana-docker/issues/170).
 
 ### v5.2.0-beta1
-* Support for Docker Secrets
+* Added support for Docker secrets.
 
 ### v5.1.0
-* Major restructuring of the container
-* Usage of `chown` removed
-* File permissions incompatibility with previous versions
-  * user id changed from 104 to 472
-  * group id changed from 107 to 472
-* Runs as the grafana user by default (instead of root)
-* All default volumes removed
+* Major restructuring of the container.
+* Removed usage of `chown`.
+* Fixed file permissions incompatibility with previous versions.
+  * user id changed from 104 to 472.
+  * group id changed from 107 to 472.
+* Runs as the Grafana user by default (instead of root).
+* Removed all default volumes.
 
 ### v4.2.0
-* Plugins are now installed into ${GF_PATHS_PLUGINS}
-* Building the container now requires a full url to the deb package instead of just version
-* Fixes bug caused by installing multiple plugins
+* Plugins are now installed into ${GF_PATHS_PLUGINS}.
+* Building the container now requires a full URL to the Debian package instead of just the version.
+* Fixed bug caused by installing multiple plugins.
 
 ### v4.0.0-beta2
-* Plugins dir (`/var/lib/grafana/plugins`) is no longer a separate volume
+* Plugins dir (`/var/lib/grafana/plugins`) is no longer a separate volume.
 
 ### v3.1.1
-* Make it possible to install specific plugin version https://github.com/grafana/grafana-docker/issues/59#issuecomment-260584026
+* Made it possible to install specific plugin version https://github.com/grafana/grafana-docker/issues/59#issuecomment-260584026.