* remove rarely-used docs/contributing.mdx page and redirect links to
docs/development/contributing.mdx
* softlink docs/development/contributing.mdx to CONTRIBUTING.md
* add back section of towncrier to CONTRIBUTING.md
* use indirect hyperlinks for all URLs in CONTRIBUTING.md
* specify that the added ports belong to livekit's container in
TURN section, and remind firewall rules for them
* prioritize the network_mode: host workaround
* add docker livelogs instructions
* use bash for code blocks instead of console
* some other small fixes
* add link to matrix-rtc room
* include livekit key-secret pair examples for clarity with livekit.yaml
* troubleshooting: add common EC errors and docker networking subsections
* fix a merge conflict issue