Update "features" section in README (#346)

* Modify "feature" section in README

Change wording in feature section to indicate that there are some
crate features that need to be enabled before they can be utilized

Signed-off-by: Shehriyar Qureshi <[email protected]>

* Run markdownlinter on README.md

Signed-off-by: Shehriyar Qureshi <[email protected]>

* Add link for push metrics word

Link to push metrics documentation in prometheus docs to show what
push metrics support actually is

Signed-off-by: Shehriyar Qureshi <[email protected]>

* Apply suggestions from code review

Co-authored-by: Luca Bruno <[email protected]>
Signed-off-by: Shehriyar Qureshi <[email protected]>

Co-authored-by: Luca Bruno <[email protected]>

Author: thatdevsherry

README.md

@@ -8,27 +8,24 @@ This is the [Rust](https://www.rust-lang.org) client library for
 [Prometheus](http://prometheus.io). The main data structures and APIs are ported
 from [Go client](https://github.com/prometheus/client_golang).
 
-
 ## Documentation
 
-Find the latest documentation at https://docs.rs/prometheus
-
+Find the latest documentation at <https://docs.rs/prometheus>.
 
 ## Advanced
 
-### Features
+### Crate features
 
-This library supports four features:
+This crate provides several optional components which can be enabled via [Cargo `[features]`](https://doc.rust-lang.org/cargo/reference/features.html):
 
 - `gen`: To generate protobuf client with the latest protobuf version instead of
   using the pre-generated client.
 
 - `nightly`: Enable nightly only features.
 
-- `process`: For collecting process info.
-
-- `push`: Enable push support.
+- `process`: Enable [process metrics](https://prometheus.io/docs/instrumenting/writing_clientlibs/#process-metrics) support.
 
+- `push`: Enable [push metrics](https://prometheus.io/docs/instrumenting/pushing/) support.
 
 ### Static Metric
 
@@ -38,7 +35,6 @@ prometheus-static-metric reduces the overhead of retrieving the concrete
 
 See [static-metric](./static-metric) directory for details.
 
-
 ## Thanks
 
 - [brian-brazil](https://github.com/brian-brazil)