Minor typos in nrpe Overview page

[John Marshall]

On https://charmhub.io/nrpe in the Overview page:

1) In the "Principal Relations" section, the text "It can also list checks that is has configured by listing them" should likely be "It can also list checks that it has configured by listing them".

2) In the "Monitors yaml" section, the text "The list of monitors past down the monitors relation" should likely be "The list of monitors passed to the monitors relation".

[Eric Chen (eric-chen)]

migrate https://github.com/canonical/charm-nrpe/issues/92