(docs) update containers.md (#340)
(docs) update containers.md (#340)

- wrap lines to make it easier to read from CLI
- format markdown (header spacing and code fences language syntax)
- correct spelling
- attempt to improve readability

### `uwsgi` v.s. `uWSGI`

uWSGI is a software application that "aims at developing a full stack for
building hosting services". It is named after the Web Server Gateway Interface,
which was the first plugin supported by the project. uwsgi is the native binary
protocol that uWSGI uses to communicate with other servers
singularityhub/sregistry,singularityhub/sregistry,singularityhub/sregistry,singularityhub/sregistry