Fix various typos in docs (#17114)

### Pull Request Checklist

<!-- Please read
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* [X] Pull request is based on the develop branch
* [X] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [X] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

docs/setup/installation.md

@@ -259,9 +259,9 @@ users, etc.) to the developers via the `--report-stats` argument.
 
 This command will generate you a config file that you can then customise, but it will
 also generate a set of keys for you. These keys will allow your homeserver to
-identify itself to other homeserver, so don't lose or delete them. It would be
+identify itself to other homeservers, so don't lose or delete them. It would be
 wise to back them up somewhere safe. (If, for whatever reason, you do need to
-change your homeserver's keys, you may find that other homeserver have the
+change your homeserver's keys, you may find that other homeservers have the
 old key cached. If you update the signing key, you should change the name of the
 key in the `<server name>.signing.key` file (the second word) to something
 different. See the [spec](https://matrix.org/docs/spec/server_server/latest.html#retrieving-server-keys) for more information on key management).