Create hashing.md (#1762)

* Create hashing.md

I wrote this up to answer some questions about hashing I've been seeing in #help.  It would be nice to add a !hash macro that could reference this as well.

* Update hashing.md

docs/extras/hashing.md

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+# Hash Keys
+
+## What are hash keys for?
+Hashkeys allow your client program (in this case RocketMap) to access the latest API. Accessing Niantic's servers without using a hashkey is using an older API that is easier for Niantic to flag and ban.
+
+## Where do I get a hash key?
+[Check out this FAQ](https://talk.pogodev.org/d/55-api-hashing-service-f-a-q)
+
+## How many RPMs will I use?
+There is no perfect way to know. There are many variables that must be considered.  Including your step size, spawn spoints, encounters.
+
+Please don't ask *"What if my step size is _x_, and I have encounters for _y_ Pokemon"*
+
+We still don't know.  Get a key, turn on your map and see if it works.
+If you are getting rate limited then either get more keys, or lower your calls (disabling/reducing encounters, disabling gym details, and decreasing step size are a few ways to reduce calls)
+
+## What does HashingQuotaExceededException('429: Request limited, error: ',) mean?
+Any variant of this means you've exceeded the Requests Per Minute that your hashing key allows
+
+## How about [ WARNING] Exception while downloading map: HashingOfflineException('502 Server Error',)
+Hashing server is temporarily unavailable (possibly offline).
+
+## And this one? BadHashRequestException('400: Bad request, error: Unauthorized',)
+Either your key is expired, or the hashing servers are having issues.
+
+## This one? TempHashingBanException('Your IP was temporarily banned for sending too many requests with invalid keys',)
+You are using invalid keys, or... you guessed it, the hashing servers are having issues