chore(protocol): Add protocol documentation (#87)

* chore(protocol): Add protocol documentation

src/protocol/README.md

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+## Description of protocol
+
+This is not a complete description, but describes the very basics. Contributions
+are welcome.
+
+There are two versions of protocol used. One is older and used for legacy purposes,
+and a newer version currently used.
+
+Both protocols have a header and include at least two fields: type and length.
+All the types and what kind of data it includes are described in
+SFSCommunication.h. The format in the comments are:
+
+- name:\[bits\], where the bits part describes how many bits is included. Since
+you are most likely running this on modern hardware, these will always be a
+multiple of 8, so think of them as how many bytes it includes (8 for 1 byte, 16
+for 2 etc.). As for the exact type, it's not described and you must look at the
+implementation code (mostly it's some type of unsigned integer).
+- name:STDSTRING, where the data type is a string
+- name:(N * \[various data\]), represents a vector for various data types
+
+All multi-byte values are ordered big-endian.
+
+### V1 protocol
+
+The first version of the protocol uses a data type and length fields as its
+header fields, both of which are 32-bit integers (may be both unsigned and
+signed). The length field indicates the length of the data after the header.
+
+Strings include a 8, 16 or 32-bit integer before the string to indicate the size
+of the string. The string does not end with a NULL byte.
+
+### V2 protocol
+
+In this new version, the length is the sum of the version and data lengths.
+The version field is a 32-byte unsigned integer.
+
+These are prefixed by "SAU" in SFSCommunication.h, and includes several changes
+to the first protocol:
+
+- String lengths are always 32-bit unsigned integers.
+- Strings end with a NULL byte.
+- Vectors and other collections include a 32-bit integer for indicating length.
+
+In addition, the packet types can have multiple versions, which is indicated
+by `version==N`. The default version is 0.