Fix markdown in configuration document

**Type**: string\

**Required**: if using S3 for uploaded media\

**Format**: URL\

**Example**: "https://s3.example.com/bucket/path"\

**Example**: "https://s3.example.com/bucket/path"

A URL to an S3 or S3-like API, including any region and bucket names, and any path in the 

bucket to append.

### S3_MEDIA_KEY

**Type**: string\

**Required**: if using S3 for uploaded media\

**Required**: if using S3 for uploaded media

An access key allowing write access to the S3 endpoint given by 

[**S3_MEDIA_ENDPOINT**](#s3_media_endpoint).

### S3_MEDIA_SECRET

**Type**: string\

**Required**: if using S3 for uploaded media\

**Required**: if using S3 for uploaded media

The secret paired with the access key given in [**S3_MEDIA_KEY**](#s3_media_key).

**Type**: string\

**Required**: no\

**Format**: URL\

**Example**: "https://my.domain.example.org/"\

**Example**: "https://my.domain.example.org/"

A base URL for viewers to access uploaded media.  This allows caching proxies, such as CDNs, 

to be used for accessing files.

### SANDBOX_MODE

**Type**: flag\

**Required**: no\

**Required**: no

If set, [sandbox mode](sandbox-mode.md) is enabled.