- Deleted credentials.json which because it is replaced by creds.yml

- Updated mkdocs to have a reference to creds-guide and migration-guide
- Updated credentials.json references to say creds.yml and have proper yml formatting

src/NadekoBot/credentials.json

@@ -1,32 +0,0 @@
-{
-  "Token": "",
-  "OwnerIds": [
-    105635576866156544
-  ],
-  "LoLApiKey": "",
-  "GoogleApiKey": "",
-  "MashapeKey": "",
-  "OsuApiKey": "",
-  "SoundCloudClientId": "",
-  "CleverbotApiKey": "",
-  "CarbonKey": "",
-  "Db": {
-    "Type": "sqlite",
-    "ConnectionString": "Data Source=data/NadekoBot.db"
-  },
-  "TotalShards": 1,
-  "PatreonAccessToken": "",
-  "PatreonCampaignId": "334038",
-  "RestartCommand": null,
-  "ShardRunCommand": "",
-  "ShardRunArguments": "",
-  "ShardRunPort": null,
-  "BotListToken": null,
-  "TwitchClientId": null,
-  "VotesToken": null,
-  "VotesUrl": null,
-  "RedisOptions": null,
-  "LocationIqApiKey": null,
-  "TimezoneDbApiKey": null,
-  "CoinmarketcapApiKey": null
-}