Addressed comments and added a basic doc

docs/snapshots.md

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+# WASM Snapshot Functionality
+
+Wasmer now supports snapshots of the current running process into a journal
+log file which allows for the resumption from an earlier point in time.
+
+# Triggers
+
+Various triggers are possible that will cause a snapshot to be taken at
+a specific point in time, these are:
+
+## On Idle
+
+Triggered when all the threads in the process goes idle.
+
+## On Listen
+
+Triggered when a listen syscall is invoked on a socket.
+    
+## On Stdin
+
+Triggered when the process reads stdin for the first time
+
+## On Timer
+
+Triggered periodically based on a timer (default 10 seconds) which can be specified using the `snapshot-timer` option
+
+## On Sigint (Ctrl+C)
+
+Issued if the user sends an interrupt signal (Ctrl + C).
+
+## On Sigalrm
+
+Alarm clock signal (used for timers)
+(see `man alarm`)
+
+## On Sigtstp
+
+The SIGTSTP signal is sent to a process by its controlling terminal to request it to stop temporarily. It is commonly initiated by the user pressing Ctrl-Z.
+
+# On Sigstop
+
+The SIGSTOP signal instructs the operating system to stop a process for later resumption
+
+# On Non Deterministic Call
+
+When a non-determinstic call is made from WASM
+
+# Limitations
+
+- The WASM process must have had the `asyncify` post processing step applied to the binary.
+- Taking a snapshot can consume large amounts of memory while its processing.
+- Snapshots are not instant and have overhead when generating.
+- The layout of the memory must be known by the runtime in order to take snapshots.
+
+# Design
+
+On startup if the restore snapshot file is specified then the runtime will restore the
+state of the WASM process by reading and processing the log entries in the snapshot
+journal. This restoration will bring the memory and the thread stacks back to a previous
+point in time and then resume all the threads.
+
+When a trigger occurs a new snapshot will be taken of the WASM process which will
+take the following steps:
+
+1. Pause all threads
+2. Capture the stack of each thread
+3. Write the thread state to the journal
+4. Write the memory (excluding stacks) to the journal
+5. Resume execution.
+
+The implementation is currently able to save and restore the following:
+
+- WASM Memory
+- Stack memory
+- Call stack
+- Open sockets
+- Open files
+- Terminal text