Add a basic readme

src/fprime_gds/common/sequence/README.md

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+# FPy Advanced Sequencing Language Version 0.1
+The FPy advanced sequencing language is a combination of a high-level scripting language and a low-level bytecode language for running complex command sequences on spacecraft flight software.
+## FPy Syntax
+### Modules, components, channels, commands and types
+You can imagine the FPy syntax as Python with the following mappings:
+1. FPrime modules become Python namespaces
+2. FPrime components become Python classes
+3. FPrime types (structs, arrays and enums) become Python classes
+4. FPrime component instances become Python object instances
+5. FPrime commands become member functions of Python object instances
+6. FPrime telemetry channels become member properties of Python object instances
+
+FPrime declaration:
+```
+module Ref {
+    passive component ExampleComponent {
+        telemetry testChannel: U8
+        sync command TEST_COMMAND(arg: string size 40)
+    }
+
+    instance exampleInstance: ExampleComponent base id 0x01
+}
+```
+FPy usage:
+```py
+# reference a telemetry channel
+Ref.exampleInstance.testChannel
+# call a command
+Ref.exampleInstance.TEST_COMMAND("arg value")
+```
+
+
+FPrime declaration:
+```
+struct ExampleStruct {
+    member: F32
+}
+
+enum TestEnum {
+    ONE
+    TWO
+    THREE
+}
+
+array TestArray = [3] U8
+```
+
+FPy usage:
+```py
+# construct a struct
+ExampleStruct(0.0)
+# reference an enum const
+TestEnum.THREE
+# construct an array
+TestArray(1, 2, 3)
+```
+
+### Sequence directives
+FPy also has sequence directives, which are like commands that control the running sequence itself.
+
+The most common sequence directives are absolute and relative sleep:
+```py
+sleep_abs(Time(time_base, time_context, seconds, useconds))
+sleep_rel(Time(time_base, time_context, seconds, useconds))
+```
+
+Due to the nature of the FPrime `CmdSequencer`, you can only have zero or one `sleep` directives before each command.
+
+## FPy Usage
+```
+fprime-seq <sequence.fpy> -d <TopologyDictionary.json> [-o <output.bin>]
+
+A compiler for the FPrime advanced sequencing language
+
+positional arguments:
+  input                 The path of the input sequence to compile
+
+options:
+  -h, --help            show this help message and exit
+  -d DICTIONARY, --dictionary DICTIONARY
+                        The JSON topology dictionary to compile against
+  -o OUTPUT, --output OUTPUT
+                        The output .bin file path. Defaults to the input file path
+```
+
+The result is a sequence binary file that works with the FPrime `CmdSequencer`.