docs: add concepts section

old-commit-hash: 5ebc65f254f66ff13c679f9f699a92458c41aa8a

docs/concepts/glossary.md

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+# openpilot glossary
+
+* **route**:
+* **segment**: routes are split into one minute chunks called segments.
+* **panda**: this is . See the repo.
+* **onroad**:
+* **offroad**:
+* **comma 3X**:

docs/concepts/logs.md

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+# Logging
+
+openpilot records routes in one minute chunks called segments. A route starts on the rising edge of ignition and ends on the falling edge.
+
+Check out our [Python library](https://github.com/commaai/openpilot/blob/master/tools/lib/logreader.py) for reading openpilot logs. Also checkout our [tools](https://github.com/commaai/openpilot/tree/master/tools) to replay and view your data. These are the same tools we use to debug and develop openpilot.
+
+For each segment, openpilot records the following log types:
+
+## rlog.bz2
+
+rlogs contain all the messages passed amongst openpilot's processes. See [cereal/services.py](https://github.com/commaai/cereal/blob/master/services.py) for a list of all the logged services. They're a bzip2 archive of the serialized capnproto messages.
+
+## {f,e,d}camera.hevc
+
+Each camera stream is H.265 encoded and written to its respective file.
+
+* `fcamera.hevc` is the road camera
+* `ecamera.hevc` is the wide road camera
+* `dcamera.hevc` is the driver camera
+
+## qlog.bz2 & qcamera.ts
+
+qlogs are a decimated subset of the rlogs. Check out [cereal/services.py](https://github.com/commaai/cereal/blob/master/services.py) for the decimation.
+
+
+qcameras are H.264 encoded, lower res versions of the fcamera.hevc. The video shown in [comma connect](https://connect.comma.ai/) is from the qcameras.
+
+
+qlogs and qcameras are designed to be small enough to upload instantly on slow internet and store forever, yet useful enough for most analysis and debugging.

docs/concepts/safety.md

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+../SAFETY.md

docs/how-to/replay-a-drive.md

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+# Replay
+
+Replaying is a critical tool for openpilot development and debugging.
+
+## Replaying a route
+*Hardware required: none*
+
+Just run `tools/replay/replay --demo`.
+
+## Replaying CAN data
+*Hardware required: jungle and comma 3/3X*
+
+1. Connect your PC to a jungle.
+2.