README|doc: fix typos/reword

Fix a few typos and reword several sentences.

README.md

@@ -9,8 +9,8 @@ See the original use-case [here](docs/use-cases/network-telemetry-nfacctd.md).
 
 :warning: `sfunnel` is still in an early development stage.
 
-:no_entry: severe performance degradation when TCP connections are funneled over
-TCP and UDP is being investigated (GSO/TSO). Do not use it.
+:no_entry: severe performance degradation when funneling TCP over TCP/UDP is
+being investigated (GSO/TSO issues). Do not use it for real traffic.
 
 ## At a glance
 

docs/use-cases/network-telemetry-nfacctd.md

@@ -139,9 +139,9 @@ _Note: this was added later on, and was not part of the original prototype_
 
 At the same time, and in order to properly traverse NATs, during funneling the
 original L4 checksum is adjusted with `src_ip` and `dst_ip` set to a known value
-(`0x0`). This allows the unfunneling to readjust the checksum based on the diff
-between `0x0` and the acutal IP addresses of the packet then, without the need
-to pass extra state within the packet.
+(`0x0`). This allows the unfunneling code to readjust the checksum based on the
+diff between the known value `0x0` and the actual IP addresses of the packet at
+this point, without the need to pass extra state within the packet.
 
 #### Using an init container