message: docs: minor typo and grammar fixups
  Minor fixups for the xDS protocol documentation.
diff: @@ -147,7 +147,7 @@ management server will provide the complete state of the LDS/CDS resources in
  each response. An absent `Listener` or `Cluster` will be deleted.
  For EDS/RDS, the management server does not need to supply every requested
  -resource and may also supply additional, unrequested resources, `resource_names`
  +resource and may also supply additional, unrequested resources. `resource_names`
  is only a hint. Envoy will silently ignore any superfluous resources. When a
  requested resource is missing in a RDS or EDS update, Envoy will retain the last
  known value for this resource. The management server may be able to infer all
  @@ -166,7 +166,7 @@ For EDS/RDS, Envoy may either generate a distinct stream for each resource of a
  given type (e.g. if each `ConfigSource` has its own distinct upstream cluster
  for a management server), or may combine together multiple resource requests for
  a given resource type when they are destined for the same management server.
  -This is left to implementation specifics, management servers should be capable
  +While this is left to implementation specifics, management servers should be capable
  of handling one or more `resource_names` for a given resource type in each
  request. Both sequence diagrams below are valid for fetching two EDS resources
  `{foo, bar}`:
  @@ -287,7 +287,7 @@ admin:
  ### Incremental xDS
  -Incremental xDS is separate xDS endpoint available for ADS, CDS and RDS that
  +Incremental xDS is a separate xDS endpoint available for ADS, CDS and RDS that
  allows:
  * Incremental updates of the list of tracked resources by the xDS client.
  @@ -295,7 +295,7 @@ allows:
  example, this may occur when a request corresponding to an unknown cluster
  arrives.
  * The xDS server can incremetally update the resources on the client.
  - This support the goal of scalability of xDS resources. Rather than deliver
  + This supports the goal of scalability of xDS resources. Rather than deliver
  all 100k clusters when a single cluster is modified, the management server
  only needs to deliver the single cluster that changed.
  @@ -319,7 +319,7 @@ debugging purposes only.
  This can be done to dynamically add or remove elements from the tracked
  `resource_names` set. In this case `response_nonce` must be omitted.
  -In this first example the client connects and receive a first update that it
  +In this first example the client connects and receives a first update that it
  ACKs. The second update fails and the client NACKs the update. Later the xDS
  client spontaneously requests the "wc" resource.
  